algorithm.py

#
# Copyright 2015 Quantopian, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from collections import Iterable
try:
    # optional cython based OrderedDict
    from cyordereddict import OrderedDict
except ImportError:
    from collections import OrderedDict
from copy import copy
import operator as op
import warnings
from datetime import tzinfo, time
import logbook
import pytz
import pandas as pd
from contextlib2 import ExitStack
from pandas.tseries.tools import normalize_date
import numpy as np

from itertools import chain, repeat
from numbers import Integral

from six import (
    exec_,
    iteritems,
    itervalues,
    string_types,
    viewkeys,
    viewvalues,
)

from zipline._protocol import handle_non_market_minutes
from zipline.assets.synthetic import make_simple_equity_info
from zipline.data.data_portal import DataPortal
from zipline.data.us_equity_pricing import PanelBarReader
from zipline.errors import (
    AttachPipelineAfterInitialize,
    HistoryInInitialize,
    NoSuchPipeline,
    OrderDuringInitialize,
    PipelineOutputDuringInitialize,
    RegisterAccountControlPostInit,
    RegisterTradingControlPostInit,
    SetBenchmarkOutsideInitialize,
    SetCommissionPostInit,
    SetSlippagePostInit,
    UnsupportedCommissionModel,
    UnsupportedDatetimeFormat,
    UnsupportedOrderParameters,
    UnsupportedSlippageModel,
    CannotOrderDelistedAsset,
    UnsupportedCancelPolicy,
    SetCancelPolicyPostInit,
    OrderInBeforeTradingStart
)
from zipline.finance.trading import TradingEnvironment
from zipline.finance.blotter import Blotter
from zipline.finance.commission import PerShare, CommissionModel
from zipline.finance.controls import (
    LongOnly,
    MaxOrderCount,
    MaxOrderSize,
    MaxPositionSize,
    MaxLeverage,
    RestrictedListOrder
)
from zipline.finance.execution import (
    LimitOrder,
    MarketOrder,
    StopLimitOrder,
    StopOrder,
)
from zipline.finance.performance import PerformanceTracker
from zipline.finance.asset_restrictions import Restrictions
from zipline.finance.slippage import (
    VolumeShareSlippage,
    SlippageModel
)
from zipline.finance.cancel_policy import NeverCancel, CancelPolicy
from zipline.finance.asset_restrictions import (
    NoRestrictions,
    StaticRestrictions,
    SecurityListRestrictions,
)
from zipline.assets import Asset, Future
from zipline.gens.tradesimulation import AlgorithmSimulator
from zipline.pipeline import Pipeline
from zipline.pipeline.engine import (
    ExplodingPipelineEngine,
    SimplePipelineEngine,
)
from zipline.utils.api_support import (
    api_method,
    require_initialized,
    require_not_initialized,
    ZiplineAPI,
    disallowed_in_before_trading_start)
from zipline.utils.input_validation import (
    coerce_string,
    ensure_upper_case,
    error_keywords,
    expect_types,
    optional,
)
from zipline.utils.calendars.trading_calendar import days_at_time
from zipline.utils.cache import CachedObject, Expired
from zipline.utils.calendars import get_calendar
from zipline.utils.compat import exc_clear

import zipline.utils.events
from zipline.utils.events import (
    EventManager,
    make_eventrule,
    date_rules,
    time_rules,
    AfterOpen,
    BeforeClose
)
from zipline.utils.factory import create_simulation_parameters
from zipline.utils.math_utils import (
    tolerant_equals,
    round_if_near_integer
)
from zipline.utils.pandas_utils import clear_dataframe_indexer_caches
from zipline.utils.preprocess import preprocess
from zipline.utils.security_list import SecurityList

import zipline.protocol
from zipline.sources.requests_csv import PandasRequestsCSV

from zipline.gens.sim_engine import MinuteSimulationClock
from zipline.sources.benchmark_source import BenchmarkSource
from zipline.zipline_warnings import ZiplineDeprecationWarning


log = logbook.Logger("ZiplineLog")


class TradingAlgorithm(object):
    """A class that represents a trading strategy and parameters to execute
    the strategy.

    Parameters
    ----------
    *args, **kwargs
        Forwarded to ``initialize`` unless listed below.
    initialize : callable[context -> None], optional
        Function that is called at the start of the simulation to
        setup the initial context.
    handle_data : callable[(context, data) -> None], optional
        Function called on every bar. This is where most logic should be
        implemented.
    before_trading_start : callable[(context, data) -> None], optional
        Function that is called before any bars have been processed each
        day.
    analyze : callable[(context, DataFrame) -> None], optional
        Function that is called at the end of the backtest. This is passed
        the context and the performance results for the backtest.
    script : str, optional
        Algoscript that contains the definitions for the four algorithm
        lifecycle functions and any supporting code.
    namespace : dict, optional
        The namespace to execute the algoscript in. By default this is an
        empty namespace that will include only python built ins.
    algo_filename : str, optional
        The filename for the algoscript. This will be used in exception
        tracebacks. default: '<string>'.
    data_frequency : {'daily', 'minute'}, optional
        The duration of the bars.
    instant_fill : bool, optional
        Whether to fill orders immediately or on next bar. default: False
    equities_metadata : dict or DataFrame or file-like object, optional
        If dict is provided, it must have the following structure:
        * keys are the identifiers
        * values are dicts containing the metadata, with the metadata
          field name as the key
        If pandas.DataFrame is provided, it must have the
        following structure:
        * column names must be the metadata fields
        * index must be the different asset identifiers
        * array contents should be the metadata value
        If an object with a ``read`` method is provided, ``read`` must
        return rows containing at least one of 'sid' or 'symbol' along
        with the other metadata fields.
    futures_metadata : dict or DataFrame or file-like object, optional
        The same layout as ``equities_metadata`` except that it is used
        for futures information.
    identifiers : list, optional
        Any asset identifiers that are not provided in the
        equities_metadata, but will be traded by this TradingAlgorithm.
    get_pipeline_loader : callable[BoundColumn -> PipelineLoader], optional
        The function that maps pipeline columns to their loaders.
    create_event_context : callable[BarData -> context manager], optional
        A function used to create a context mananger that wraps the
        execution of all events that are scheduled for a bar.
        This function will be passed the data for the bar and should
        return the actual context manager that will be entered.
    history_container_class : type, optional
        The type of history container to use. default: HistoryContainer
    platform : str, optional
        The platform the simulation is running on. This can be queried for
        in the simulation with ``get_environment``. This allows algorithms
        to conditionally execute code based on platform it is running on.
        default: 'zipline'
    """

    def __init__(self, *args, **kwargs):
        """Initialize sids and other state variables.

        :Arguments:
        :Optional:
            initialize : function
                Function that is called with a single
                argument at the begninning of the simulation.
            handle_data : function
                Function that is called with 2 arguments
                (context and data) on every bar.
            script : str
                Algoscript that contains initialize and
                handle_data function definition.
            data_frequency : {'daily', 'minute'}
               The duration of the bars.
            capital_base : float <default: 1.0e5>
               How much capital to start with.
            asset_finder : An AssetFinder object
                A new AssetFinder object to be used in this TradingEnvironment
            equities_metadata : can be either:
                            - dict
                            - pandas.DataFrame
                            - object with 'read' property
                If dict is provided, it must have the following structure:
                * keys are the identifiers
                * values are dicts containing the metadata, with the metadata
                  field name as the key
                If pandas.DataFrame is provided, it must have the
                following structure:
                * column names must be the metadata fields
                * index must be the different asset identifiers
                * array contents should be the metadata value
                If an object with a 'read' property is provided, 'read' must
                return rows containing at least one of 'sid' or 'symbol' along
                with the other metadata fields.
            identifiers : List
                Any asset identifiers that are not provided in the
                equities_metadata, but will be traded by this TradingAlgorithm
        """
        self.sources = []

        # List of trading controls to be used to validate orders.
        self.trading_controls = []

        # List of account controls to be checked on each bar.
        self.account_controls = []

        self._recorded_vars = {}
        self.namespace = kwargs.pop('namespace', {})

        self._platform = kwargs.pop('platform', 'zipline')

        self.logger = None

        self.data_portal = kwargs.pop('data_portal', None)

        # If an env has been provided, pop it
        self.trading_environment = kwargs.pop('env', None)

        if self.trading_environment is None:
            self.trading_environment = TradingEnvironment()

        # Update the TradingEnvironment with the provided asset metadata
        if 'equities_metadata' in kwargs or 'futures_metadata' in kwargs:
            warnings.warn(
                'passing metadata to TradingAlgorithm is deprecated; please'
                ' write this data into the asset db before passing it to the'
                ' trading environment',
                DeprecationWarning,
                stacklevel=1,
            )
            self.trading_environment.write_data(
                equities=kwargs.pop('equities_metadata', None),
                futures=kwargs.pop('futures_metadata', None),
            )

        # If a schedule has been provided, pop it. Otherwise, use NYSE.
        self.trading_calendar = kwargs.pop(
            'trading_calendar',
            get_calendar("NYSE")
        )

        self.sim_params = kwargs.pop('sim_params', None)
        if self.sim_params is None:
            self.sim_params = create_simulation_parameters(
                start=kwargs.pop('start', None),
                end=kwargs.pop('end', None),
                trading_calendar=self.trading_calendar,
            )

        self.perf_tracker = None
        # Pull in the environment's new AssetFinder for quick reference
        self.asset_finder = self.trading_environment.asset_finder

        # Initialize Pipeline API data.
        self.init_engine(kwargs.pop('get_pipeline_loader', None))
        self._pipelines = {}
        # Create an always-expired cache so that we compute the first time data
        # is requested.
        self._pipeline_cache = CachedObject(None, pd.Timestamp(0, tz='UTC'))

        self.blotter = kwargs.pop('blotter', None)
        self.cancel_policy = kwargs.pop('cancel_policy', NeverCancel())
        if not self.blotter:
            self.blotter = Blotter(
                data_frequency=self.data_frequency,
                asset_finder=self.asset_finder,
                slippage_func=VolumeShareSlippage(),
                commission=PerShare(),
                # Default to NeverCancel in zipline
                cancel_policy=self.cancel_policy
            )

        # The symbol lookup date specifies the date to use when resolving
        # symbols to sids, and can be set using set_symbol_lookup_date()
        self._symbol_lookup_date = None

        self.portfolio_needs_update = True
        self.account_needs_update = True
        self.performance_needs_update = True
        self._portfolio = None
        self._account = None

        # If string is passed in, execute and get reference to
        # functions.
        self.algoscript = kwargs.pop('script', None)

        self._initialize = None
        self._before_trading_start = None
        self._analyze = None

        self._in_before_trading_start = False

        self.event_manager = EventManager(
            create_context=kwargs.pop('create_event_context', None),
        )

        self._handle_data = None

        def noop(*args, **kwargs):
            pass

        if self.algoscript is not None:
            api_methods = {
                'initialize',
                'handle_data',
                'before_trading_start',
                'analyze',
            }
            unexpected_api_methods = viewkeys(kwargs) & api_methods
            if unexpected_api_methods:
                raise ValueError(
                    "TradingAlgorithm received a script and the following API"
                    " methods as functions:\n{funcs}".format(
                        funcs=unexpected_api_methods,
                    )
                )

            filename = kwargs.pop('algo_filename', None)
            if filename is None:
                filename = '<string>'
            code = compile(self.algoscript, filename, 'exec')
            exec_(code, self.namespace)

            self._initialize = self.namespace.get('initialize', noop)
            self._handle_data = self.namespace.get('handle_data', noop)
            self._before_trading_start = self.namespace.get(
                'before_trading_start',
            )
            # Optional analyze function, gets called after run
            self._analyze = self.namespace.get('analyze')

        else:
            self._initialize = kwargs.pop('initialize', noop)
            self._handle_data = kwargs.pop('handle_data', noop)
            self._before_trading_start = kwargs.pop(
                'before_trading_start',
                None,
            )
            self._analyze = kwargs.pop('analyze', None)

        self.event_manager.add_event(
            zipline.utils.events.Event(
                zipline.utils.events.Always(),
                # We pass handle_data.__func__ to get the unbound method.
                # We will explicitly pass the algorithm to bind it again.
                self.handle_data.__func__,
            ),
            prepend=True,
        )

        # Alternative way of setting data_frequency for backwards
        # compatibility.
        if 'data_frequency' in kwargs:
            self.data_frequency = kwargs.pop('data_frequency')

        # Prepare the algo for initialization
        self.initialized = False
        self.initialize_args = args
        self.initialize_kwargs = kwargs

        self.benchmark_sid = kwargs.pop('benchmark_sid', None)

        # A dictionary of capital changes, keyed by timestamp, indicating the
        # target/delta of the capital changes, along with values
        self.capital_changes = kwargs.pop('capital_changes', {})

        # A dictionary of the actual capital change deltas, keyed by timestamp
        self.capital_change_deltas = {}

        self.restrictions = NoRestrictions()

    def init_engine(self, get_loader):
        """
        Construct and store a PipelineEngine from loader.

        If get_loader is None, constructs an ExplodingPipelineEngine
        """
        if get_loader is not None:
            self.engine = SimplePipelineEngine(
                get_loader,
                self.trading_calendar.all_sessions,
                self.asset_finder,
            )
        else:
            self.engine = ExplodingPipelineEngine()

    def initialize(self, *args, **kwargs):
        """
        Call self._initialize with `self` made available to Zipline API
        functions.
        """
        with ZiplineAPI(self):
            self._initialize(self, *args, **kwargs)

    def before_trading_start(self, data):
        if self._before_trading_start is None:
            return

        self._in_before_trading_start = True

        with handle_non_market_minutes(data) if \
                self.data_frequency == "minute" else ExitStack():
            self._before_trading_start(self, data)

        self._in_before_trading_start = False

    def handle_data(self, data):
        if self._handle_data:
            self._handle_data(self, data)

        # Unlike trading controls which remain constant unless placing an
        # order, account controls can change each bar. Thus, must check
        # every bar no matter if the algorithm places an order or not.
        self.validate_account_controls()

    def analyze(self, perf):
        if self._analyze is None:
            return

        with ZiplineAPI(self):
            self._analyze(self, perf)

    def __repr__(self):
        """
        N.B. this does not yet represent a string that can be used
        to instantiate an exact copy of an algorithm.

        However, it is getting close, and provides some value as something
        that can be inspected interactively.
        """
        return """
{class_name}(
    capital_base={capital_base}
    sim_params={sim_params},
    initialized={initialized},
    slippage={slippage},
    commission={commission},
    blotter={blotter},
    recorded_vars={recorded_vars})
""".strip().format(class_name=self.__class__.__name__,
                   capital_base=self.sim_params.capital_base,
                   sim_params=repr(self.sim_params),
                   initialized=self.initialized,
                   slippage=repr(self.blotter.slippage_func),
                   commission=repr(self.blotter.commission),
                   blotter=repr(self.blotter),
                   recorded_vars=repr(self.recorded_vars))

    def _create_clock(self):
        """
        If the clock property is not set, then create one based on frequency.
        """
        trading_o_and_c = self.trading_calendar.schedule.ix[
            self.sim_params.sessions]
        market_closes = trading_o_and_c['market_close']
        minutely_emission = False

        if self.sim_params.data_frequency == 'minute':
            market_opens = trading_o_and_c['market_open']

            minutely_emission = self.sim_params.emission_rate == "minute"
        else:
            # in daily mode, we want to have one bar per session, timestamped
            # as the last minute of the session.
            market_opens = market_closes

        # The calendar's execution times are the minutes over which we actually
        # want to run the clock. Typically the execution times simply adhere to
        # the market open and close times. In the case of the futures calendar,
        # for example, we only want to simulate over a subset of the full 24
        # hour calendar, so the execution times dictate a market open time of
        # 6:31am US/Eastern and a close of 5:00pm US/Eastern.
        execution_opens = \
            self.trading_calendar.execution_time_from_open(market_opens)
        execution_closes = \
            self.trading_calendar.execution_time_from_close(market_closes)

        # FIXME generalize these values
        before_trading_start_minutes = days_at_time(
            self.sim_params.sessions,
            time(8, 45),
            "US/Eastern"
        )

        return MinuteSimulationClock(
            self.sim_params.sessions,
            execution_opens,
            execution_closes,
            before_trading_start_minutes,
            minute_emission=minutely_emission,
        )

    def _create_benchmark_source(self):
        return BenchmarkSource(
            benchmark_sid=self.benchmark_sid,
            env=self.trading_environment,
            trading_calendar=self.trading_calendar,
            sessions=self.sim_params.sessions,
            data_portal=self.data_portal,
            emission_rate=self.sim_params.emission_rate,
        )

    def _create_generator(self, sim_params):
        if sim_params is not None:
            self.sim_params = sim_params

        if self.perf_tracker is None:
            # HACK: When running with the `run` method, we set perf_tracker to
            # None so that it will be overwritten here.
            self.perf_tracker = PerformanceTracker(
                sim_params=self.sim_params,
                trading_calendar=self.trading_calendar,
                env=self.trading_environment,
            )

            # Set the dt initially to the period start by forcing it to change.
            self.on_dt_changed(self.sim_params.start_session)

        if not self.initialized:
            self.initialize(*self.initialize_args, **self.initialize_kwargs)
            self.initialized = True

        self.trading_client = AlgorithmSimulator(
            self,
            sim_params,
            self.data_portal,
            self._create_clock(),
            self._create_benchmark_source(),
            self.restrictions,
            universe_func=self._calculate_universe
        )

        return self.trading_client.transform()

    def _calculate_universe(self):
        # this exists to provide backwards compatibility for older,
        # deprecated APIs, particularly around the iterability of
        # BarData (ie, 'for sid in data`).

        # our universe is all the assets passed into `run`.
        return self._assets_from_source

    def get_generator(self):
        """
        Override this method to add new logic to the construction
        of the generator. Overrides can use the _create_generator
        method to get a standard construction generator.
        """
        return self._create_generator(self.sim_params)

    def run(self, data=None, overwrite_sim_params=True):
        """Run the algorithm.

        :Arguments:
            source : DataPortal

        :Returns:
            daily_stats : pandas.DataFrame
              Daily performance metrics such as returns, alpha etc.

        """
        self._assets_from_source = []

        if isinstance(data, DataPortal):
            self.data_portal = data

            # define the universe as all the assets in the assetfinder
            # This is not great, because multiple runs can accumulate assets
            # in the assetfinder, but it's better than spending time adding
            # functionality in the dataportal to report all the assets it
            # knows about.
            self._assets_from_source = \
                self.trading_environment.asset_finder.retrieve_all(
                    self.trading_environment.asset_finder.sids
                )

        else:
            if isinstance(data, pd.DataFrame):
                # If a DataFrame is passed. Promote it to a Panel.
                # The reader will fake volume values.
                data = pd.Panel({'close': data.copy()})
                data = data.swapaxes(0, 2)

            if isinstance(data, pd.Panel):
                # Guard against tz-naive index.
                if data.major_axis.tz is None:
                    data.major_axis = data.major_axis.tz_localize('UTC')

                # For compatibility with existing examples allow start/end
                # to be inferred.
                if overwrite_sim_params:
                    self.sim_params = self.sim_params.create_new(
                        self.trading_calendar.minute_to_session_label(
                            data.major_axis[0]
                        ),
                        self.trading_calendar.minute_to_session_label(
                            data.major_axis[-1]
                        ),
                    )

                    # Assume data is daily if timestamp times are
                    # standardized, otherwise assume minute bars.
                    times = data.major_axis.time
                    if np.all(times == times[0]):
                        self.sim_params.data_frequency = 'daily'
                    else:
                        self.sim_params.data_frequency = 'minute'

                copy_panel = data.rename(
                    # These were the old names for the close/open columns.  We
                    # need to make a copy anyway, so swap these for backwards
                    # compat while we're here.
                    minor_axis={'close_price': 'close', 'open_price': 'open'},
                    copy=True,
                )
                copy_panel.items = self._write_and_map_id_index_to_sids(
                    copy_panel.items, copy_panel.major_axis[0],
                )
                self._assets_from_source = (
                    self.asset_finder.retrieve_all(
                        copy_panel.items
                    )
                )

                if self.sim_params.data_frequency == 'daily':
                    equity_reader_arg = 'equity_daily_reader'
                elif self.sim_params.data_frequency == 'minute':
                    equity_reader_arg = 'equity_minute_reader'
                equity_reader = PanelBarReader(
                    self.trading_calendar,
                    copy_panel,
                    self.sim_params.data_frequency,
                )

                self.data_portal = DataPortal(
                    self.asset_finder,
                    self.trading_calendar,
                    first_trading_day=equity_reader.first_trading_day,
                    **{equity_reader_arg: equity_reader}
                )

        # Force a reset of the performance tracker, in case
        # this is a repeat run of the algorithm.
        self.perf_tracker = None

        # Create zipline and loop through simulated_trading.
        # Each iteration returns a perf dictionary
        try:
            perfs = []
            for perf in self.get_generator():
                perfs.append(perf)

            # convert perf dict to pandas dataframe
            daily_stats = self._create_daily_stats(perfs)

            self.analyze(daily_stats)
        finally:
            self.data_portal = None

        return daily_stats

    def _write_and_map_id_index_to_sids(self, identifiers, as_of_date):
        # Build new Assets for identifiers that can't be resolved as
        # sids/Assets
        def is_unknown(asset_or_sid):
            sid = op.index(asset_or_sid)
            return self.asset_finder.retrieve_asset(
                sid=sid,
                default_none=True
            ) is None

        new_assets = set()
        new_sids = set()
        new_symbols = set()
        for identifier in identifiers:
            if isinstance(identifier, Asset) and is_unknown(identifier):
                new_assets.add(identifier)
            elif isinstance(identifier, Integral) and is_unknown(identifier):
                new_sids.add(identifier)
            elif isinstance(identifier, (string_types)):
                new_symbols.add(identifier)
            else:
                try:
                    new_sids.add(op.index(identifier))
                except TypeError:
                    raise TypeError(
                        "Can't convert %s to an asset." % identifier
                    )

        new_assets = tuple(new_assets)
        new_sids = tuple(new_sids)
        new_symbols = tuple(new_symbols)

        number_of_kinds_of_new_things = (
            sum((bool(new_assets), bool(new_sids), bool(new_symbols)))
        )

        # Nothing to insert, bail early.
        if not number_of_kinds_of_new_things:
            return self.asset_finder.map_identifier_index_to_sids(
                identifiers, as_of_date,
            )
        elif number_of_kinds_of_new_things == 1:
            warnings.warn(
                'writing unknown identifiers into the assets db of the trading'
                ' environment is deprecated; please write this information'
                ' to the assets db before constructing the environment',
                DeprecationWarning,
                stacklevel=2,
            )
        else:
            raise ValueError(
                "Mixed types in DataFrame or Panel index.\n"
                "Asset Count: %d, Sid Count: %d, Symbol Count: %d.\n"
                "Choose one type and stick with it." % (
                    len(new_assets),
                    len(new_sids),
                    len(new_symbols),
                )
            )

        def map_getattr(iterable, attr):
            return [getattr(i, attr) for i in iterable]

        if new_assets:
            frame_to_write = pd.DataFrame(
                data=dict(
                    symbol=map_getattr(new_assets, 'symbol'),
                    start_date=map_getattr(new_assets, 'start_date'),
                    end_date=map_getattr(new_assets, 'end_date'),
                    exchange=map_getattr(new_assets, 'exchange'),
                ),
                index=map_getattr(new_assets, 'sid'),
            )
        elif new_sids:
            frame_to_write = make_simple_equity_info(
                new_sids,
                start_date=self.sim_params.start_session,
                end_date=self.sim_params.end_session,
                symbols=map(str, new_sids),
            )
        elif new_symbols:
            existing_sids = self.asset_finder.sids
            first_sid = max(existing_sids) + 1 if existing_sids else 0
            fake_sids = range(first_sid, first_sid + len(new_symbols))
            frame_to_write = make_simple_equity_info(
                sids=fake_sids,
                start_date=as_of_date,
                end_date=self.sim_params.end_session,
                symbols=new_symbols,
            )
        else:
            raise AssertionError("This should never happen.")

        self.trading_environment.write_data(equities=frame_to_write)

        # We need to clear out any cache misses that were stored while trying
        # to do lookups.  The real fix for this problem is to not construct an
        # AssetFinder until we `run()` when we actually have all the data we
        # need to so.
        self.asset_finder._reset_caches()

        return self.asset_finder.map_identifier_index_to_sids(
            identifiers, as_of_date,
        )

    def _create_daily_stats(self, perfs):
        # create daily and cumulative stats dataframe
        daily_perfs = []
        # TODO: the loop here could overwrite expected properties
        # of daily_perf. Could potentially raise or log a
        # warning.
        for perf in perfs:
            if 'daily_perf' in perf:

                perf['daily_perf'].update(
                    perf['daily_perf'].pop('recorded_vars')
                )
                perf['daily_perf'].update(perf['cumulative_risk_metrics'])
                daily_perfs.append(perf['daily_perf'])
            else:
                self.risk_report = perf

        daily_dts = pd.DatetimeIndex(
            [p['period_close'] for p in daily_perfs], tz='UTC'
        )
        daily_stats = pd.DataFrame(daily_perfs, index=daily_dts)

        return daily_stats

    def calculate_capital_changes(self, dt, emission_rate, is_interday,
                                  portfolio_value_adjustment=0.0):
        """
        If there is a capital change for a given dt, this means the the change
        occurs before `handle_data` on the given dt. In the case of the
        change being a target value, the change will be computed on the
        portfolio value according to prices at the given dt

        `portfolio_value_adjustment`, if specified, will be removed from the
        portfolio_value of the cumulative performance when calculating deltas
        from target capital changes.
        """
        try:
            capital_change = self.capital_changes[dt]
        except KeyError:
            return

        if emission_rate == 'daily':
            # If we are running daily emission, prices won't
            # necessarily be synced at the end of every minute, and we
            # need the up-to-date prices for capital change
            # calculations. We want to sync the prices as of the
            # last market minute, and this is okay from a data portal
            # perspective as we have technically not "advanced" to the
            # current dt yet.
            self.perf_tracker.position_tracker.sync_last_sale_prices(
                self.trading_calendar.previous_minute(
                    dt
                ),
                False,
                self.data_portal
            )
        self.perf_tracker.prepare_capital_change(is_interday)

        if capital_change['type'] == 'target':
            target = capital_change['value']
            capital_change_amount = target - \
                (self.updated_portfolio().portfolio_value -
                 portfolio_value_adjustment)
            self.portfolio_needs_update = True

            log.info('Processing capital change to target %s at %s. Capital '
                     'change delta is %s' % (target, dt,
                                             capital_change_amount))
        elif capital_change['type'] == 'delta':
            target = None
            capital_change_amount = capital_change['value']
            log.info('Processing capital change of delta %s at %s'
                     % (capital_change_amount, dt))
        else:
            log.error("Capital change %s does not indicate a valid type "
                      "('target' or 'delta')" % capital_change)
            return

        self.capital_change_deltas.update({dt: capital_change_amount})
        self.perf_tracker.process_capital_change(capital_change_amount,
                                                 is_interday)

        yield {
            'capital_change':
                {'date': dt,
                 'type': 'cash',
                 'target': target,
                 'delta': capital_change_amount}
        }

    @api_method
    def get_environment(self, field='platform'):
        """Query the execution environment.

        Parameters
        ----------
        field : {'platform', 'arena', 'data_frequency',
                 'start', 'end', 'capital_base', 'platform', '*'}
            The field to query. The options have the following meanings:
              arena : str
                  The arena from the simulation parameters. This will normally
                  be ``'backtest'`` but some systems may use this distinguish
                  live trading from backtesting.
              data_frequency : {'daily', 'minute'}
                  data_frequency tells the algorithm if it is running with
                  daily data or minute data.
              start : datetime
                  The start date for the simulation.
              end : datetime
                  The end date for the simulation.
              capital_base : float
                  The starting capital for the simulation.
              platform : str
                  The platform that the code is running on. By default this
                  will be the string 'zipline'. This can allow algorithms to
                  know if they are running on the Quantopian platform instead.
              * : dict[str -> any]
                  Returns all of the fields in a dictionary.

        Returns
        -------
        val : any
            The value for the field queried. See above for more information.

        Raises
        ------
        ValueError
            Raised when ``field`` is not a valid option.
        """
        env = {
            'arena': self.sim_params.arena,
            'data_frequency': self.sim_params.data_frequency,
            'start': self.sim_params.first_open,
            'end': self.sim_params.last_close,
            'capital_base': self.sim_params.capital_base,
            'platform': self._platform
        }
        if field == '*':
            return env
        else:
            try:
                return env[field]
            except KeyError:
                raise ValueError(
                    '%r is not a valid field for get_environment' % field,
                )

    @api_method
    def fetch_csv(self,
                  url,
                  pre_func=None,
                  post_func=None,
                  date_column='date',
                  date_format=None,
                  timezone=pytz.utc.zone,
                  symbol=None,
                  mask=True,
                  symbol_column=None,
                  special_params_checker=None,
                  **kwargs):
        """Fetch a csv from a remote url and register the data so that it is
        queryable from the ``data`` object.

        Parameters
        ----------
        url : str
            The url of the csv file to load.
        pre_func : callable[pd.DataFrame -> pd.DataFrame], optional
            A callback to allow preprocessing the raw data returned from
            fetch_csv before dates are paresed or symbols are mapped.
        post_func : callable[pd.DataFrame -> pd.DataFrame], optional
            A callback to allow postprocessing of the data after dates and
            symbols have been mapped.
        date_column : str, optional
            The name of the column in the preprocessed dataframe containing
            datetime information to map the data.
        date_format : str, optional
            The format of the dates in the ``date_column``. If not provided
            ``fetch_csv`` will attempt to infer the format. For information
            about the format of this string, see :func:`pandas.read_csv`.
        timezone : tzinfo or str, optional
            The timezone for the datetime in the ``date_column``.
        symbol : str, optional
            If the data is about a new asset or index then this string will
            be the name used to identify the values in ``data``. For example,
            one may use ``fetch_csv`` to load data for VIX, then this field
            could be the string ``'VIX'``.
        mask : bool, optional
            Drop any rows which cannot be symbol mapped.
        symbol_column : str
            If the data is attaching some new attribute to each asset then this
            argument is the name of the column in the preprocessed dataframe
            containing the symbols. This will be used along with the date
            information to map the sids in the asset finder.
        **kwargs
            Forwarded to :func:`pandas.read_csv`.

        Returns
        -------
        csv_data_source : zipline.sources.requests_csv.PandasRequestsCSV
            A requests source that will pull data from the url specified.
        """

        # Show all the logs every time fetcher is used.
        csv_data_source = PandasRequestsCSV(
            url,
            pre_func,
            post_func,
            self.asset_finder,
            self.trading_calendar.day,
            self.sim_params.start_session,
            self.sim_params.end_session,
            date_column,
            date_format,
            timezone,
            symbol,
            mask,
            symbol_column,
            data_frequency=self.data_frequency,
            special_params_checker=special_params_checker,
            **kwargs
        )

        # ingest this into dataportal
        self.data_portal.handle_extra_source(csv_data_source.df,
                                             self.sim_params)

        return csv_data_source

    def add_event(self, rule=None, callback=None):
        """Adds an event to the algorithm's EventManager.

        Parameters
        ----------
        rule : EventRule
            The rule for when the callback should be triggered.
        callback : callable[(context, data) -> None]
            The function to execute when the rule is triggered.
        """
        self.event_manager.add_event(
            zipline.utils.events.Event(rule, callback),
        )

    @api_method
    def schedule_function(self,
                          func,
                          date_rule=None,
                          time_rule=None,
                          half_days=True,
                          calendar=None):
        """Schedules a function to be called according to some timed rules.

        Parameters
        ----------
        func : callable[(context, data) -> None]
            The function to execute when the rule is triggered.
        date_rule : EventRule, optional
            The rule for the dates to execute this function.
        time_rule : EventRule, optional
            The rule for the times to execute this function.
        half_days : bool, optional
            Should this rule fire on half days?

        See Also
        --------
        :class:`zipline.api.date_rules`
        :class:`zipline.api.time_rules`
        """

        # When the user calls schedule_function(func, <time_rule>), assume that
        # the user meant to specify a time rule but no date rule, instead of
        # a date rule and no time rule as the signature suggests
        if isinstance(date_rule, (AfterOpen, BeforeClose)) and not time_rule:
            warnings.warn('Got a time rule for the second positional argument '
                          'date_rule. You should use keyword argument '
                          'time_rule= when calling schedule_function without '
                          'specifying a date_rule', stacklevel=3)

        date_rule = date_rule or date_rules.every_day()
        time_rule = ((time_rule or time_rules.every_minute())
                     if self.sim_params.data_frequency == 'minute' else
                     # If we are in daily mode the time_rule is ignored.
                     time_rules.every_minute())

        # Check the type of the algorithm's schedule before pulling calendar
        # Note that the ExchangeTradingSchedule is currently the only
        # TradingSchedule class, so this is unlikely to be hit
        cal = calendar or self.trading_calendar

        self.add_event(
            make_eventrule(date_rule, time_rule, cal, half_days),
            func,
        )

    @api_method
    def record(self, *args, **kwargs):
        """Track and record values each day.

        Parameters
        ----------
        **kwargs
            The names and values to record.

        Notes
        -----
        These values will appear in the performance packets and the performance
        dataframe passed to ``analyze`` and returned from
        :func:`~zipline.run_algorithm`.
        """
        # Make 2 objects both referencing the same iterator
        args = [iter(args)] * 2

        # Zip generates list entries by calling `next` on each iterator it
        # receives.  In this case the two iterators are the same object, so the
        # call to next on args[0] will also advance args[1], resulting in zip
        # returning (a,b) (c,d) (e,f) rather than (a,a) (b,b) (c,c) etc.
        positionals = zip(*args)
        for name, value in chain(positionals, iteritems(kwargs)):
            self._recorded_vars[name] = value

    @api_method
    def set_benchmark(self, benchmark):
        """Set the benchmark asset.

        Parameters
        ----------
        benchmark : Asset
            The asset to set as the new benchmark.

        Notes
        -----
        Any dividends payed out for that new benchmark asset will be
        automatically reinvested.
        """
        if self.initialized:
            raise SetBenchmarkOutsideInitialize()

        self.benchmark_sid = benchmark

    @api_method
    @preprocess(symbol_str=ensure_upper_case)
    def symbol(self, symbol_str):
        """Lookup an Equity by its ticker symbol.

        Parameters
        ----------
        symbol_str : str
            The ticker symbol for the equity to lookup.

        Returns
        -------
        equity : Equity
            The equity that held the ticker symbol on the current
            symbol lookup date.

        Raises
        ------
        SymbolNotFound
            Raised when the symbols was not held on the current lookup date.

        See Also
        --------
        :func:`zipline.api.set_symbol_lookup_date`
        """
        # If the user has not set the symbol lookup date,
        # use the end_session as the date for sybmol->sid resolution.
        _lookup_date = self._symbol_lookup_date \
            if self._symbol_lookup_date is not None \
            else self.sim_params.end_session

        return self.asset_finder.lookup_symbol(
            symbol_str,
            as_of_date=_lookup_date,
        )

    @api_method
    @preprocess(root_symbol_str=ensure_upper_case)
    def continuous_future(self, root_symbol_str, offset, roll):
        """Create a specifier for a continuous contract.

        Parameters
        ----------
        root_symbol_str : str
            The root symbol for the future chain.

        offset : int
            The distance from the primary contract.

        roll_style : str
            How rolls are determined.

        Returns
        -------
        continuous_future : ContinuousFuture
            The continuous future specifier.
        """
        return self.asset_finder.create_continuous_future(
            root_symbol_str,
            offset,
            roll,
        )

    @api_method
    def symbols(self, *args):
        """Lookup multuple Equities as a list.

        Parameters
        ----------
        *args : iterable[str]
            The ticker symbols to lookup.

        Returns
        -------
        equities : list[Equity]
            The equities that held the given ticker symbols on the current
            symbol lookup date.

        Raises
        ------
        SymbolNotFound
            Raised when one of the symbols was not held on the current
            lookup date.

        See Also
        --------
        :func:`zipline.api.set_symbol_lookup_date`
        """
        return [self.symbol(identifier) for identifier in args]

    @api_method
    def sid(self, sid):
        """Lookup an Asset by its unique asset identifier.

        Parameters
        ----------
        sid : int
            The unique integer that identifies an asset.

        Returns
        -------
        asset : Asset
            The asset with the given ``sid``.

        Raises
        ------
        SidsNotFound
            When a requested ``sid`` does not map to any asset.
        """
        return self.asset_finder.retrieve_asset(sid)

    @api_method
    @preprocess(symbol=ensure_upper_case)
    def future_symbol(self, symbol):
        """Lookup a futures contract with a given symbol.

        Parameters
        ----------
        symbol : str
            The symbol of the desired contract.

        Returns
        -------
        future : Future
            The future that trades with the name ``symbol``.

        Raises
        ------
        SymbolNotFound
            Raised when no contract named 'symbol' is found.
        """
        return self.asset_finder.lookup_future_symbol(symbol)

    def _calculate_order_value_amount(self, asset, value):
        """
        Calculates how many shares/contracts to order based on the type of
        asset being ordered.
        """
        # Make sure the asset exists, and that there is a last price for it.
        # FIXME: we should use BarData's can_trade logic here, but I haven't
        # yet found a good way to do that.
        normalized_date = normalize_date(self.datetime)

        if normalized_date < asset.start_date:
            raise CannotOrderDelistedAsset(
                msg="Cannot order {0}, as it started trading on"
                    " {1}.".format(asset.symbol, asset.start_date)
            )
        elif normalized_date > asset.end_date:
            raise CannotOrderDelistedAsset(
                msg="Cannot order {0}, as it stopped trading on"
                    " {1}.".format(asset.symbol, asset.end_date)
            )
        else:
            last_price = \
                self.trading_client.current_data.current(asset, "price")

            if np.isnan(last_price):
                raise CannotOrderDelistedAsset(
                    msg="Cannot order {0} on {1} as there is no last "
                        "price for the security.".format(asset.symbol,
                                                         self.datetime)
                )

        if tolerant_equals(last_price, 0):
            zero_message = "Price of 0 for {psid}; can't infer value".format(
                psid=asset
            )
            if self.logger:
                self.logger.debug(zero_message)
            # Don't place any order
            return 0

        if isinstance(asset, Future):
            value_multiplier = asset.multiplier
        else:
            value_multiplier = 1

        return value / (last_price * value_multiplier)

    def _can_order_asset(self, asset):
        if not isinstance(asset, Asset):
            raise UnsupportedOrderParameters(
                msg="Passing non-Asset argument to 'order()' is not supported."
                    " Use 'sid()' or 'symbol()' methods to look up an Asset."
            )

        if asset.auto_close_date:
            day = normalize_date(self.get_datetime())

            if day > min(asset.end_date, asset.auto_close_date):
                # If we are after the asset's end date or auto close date, warn
                # the user that they can't place an order for this asset, and
                # return None.
                log.warn("Cannot place order for {0}, as it has de-listed. "
                         "Any existing positions for this asset will be "
                         "liquidated on "
                         "{1}.".format(asset.symbol, asset.auto_close_date))

                return False

        return True

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def order(self,
              asset,
              amount,
              limit_price=None,
              stop_price=None,
              style=None):
        """Place an order.

        Parameters
        ----------
        asset : Asset
            The asset that this order is for.
        amount : int
            The amount of shares to order. If ``amount`` is positive, this is
            the number of shares to buy or cover. If ``amount`` is negative,
            this is the number of shares to sell or short.
        limit_price : float, optional
            The limit price for the order.
        stop_price : float, optional
            The stop price for the order.
        style : ExecutionStyle, optional
            The execution style for the order.

        Returns
        -------
        order_id : str or None
            The unique identifier for this order, or None if no order was
            placed.

        Notes
        -----
        The ``limit_price`` and ``stop_price`` arguments provide shorthands for
        passing common execution styles. Passing ``limit_price=N`` is
        equivalent to ``style=LimitOrder(N)``. Similarly, passing
        ``stop_price=M`` is equivalent to ``style=StopOrder(M)``, and passing
        ``limit_price=N`` and ``stop_price=M`` is equivalent to
        ``style=StopLimitOrder(N, M)``. It is an error to pass both a ``style``
        and ``limit_price`` or ``stop_price``.

        See Also
        --------
        :class:`zipline.finance.execution.ExecutionStyle`
        :func:`zipline.api.order_value`
        :func:`zipline.api.order_percent`
        """
        if not self._can_order_asset(asset):
            return None

        amount, style = self._calculate_order(asset, amount,
                                              limit_price, stop_price, style)
        return self.blotter.order(asset, amount, style)

    def _calculate_order(self, asset, amount,
                         limit_price=None, stop_price=None, style=None):
        # Truncate to the integer share count that's either within .0001 of
        # amount or closer to zero.
        # E.g. 3.9999 -> 4.0; 5.5 -> 5.0; -5.5 -> -5.0
        amount = int(round_if_near_integer(amount))

        # Raises a ZiplineError if invalid parameters are detected.
        self.validate_order_params(asset,
                                   amount,
                                   limit_price,
                                   stop_price,
                                   style)

        # Convert deprecated limit_price and stop_price parameters to use
        # ExecutionStyle objects.
        style = self.__convert_order_params_for_blotter(limit_price,
                                                        stop_price,
                                                        style)
        return amount, style

    def validate_order_params(self,
                              asset,
                              amount,
                              limit_price,
                              stop_price,
                              style):
        """
        Helper method for validating parameters to the order API function.

        Raises an UnsupportedOrderParameters if invalid arguments are found.
        """

        if not self.initialized:
            raise OrderDuringInitialize(
                msg="order() can only be called from within handle_data()"
            )

        if style:
            if limit_price:
                raise UnsupportedOrderParameters(
                    msg="Passing both limit_price and style is not supported."
                )

            if stop_price:
                raise UnsupportedOrderParameters(
                    msg="Passing both stop_price and style is not supported."
                )

        for control in self.trading_controls:
            control.validate(asset,
                             amount,
                             self.updated_portfolio(),
                             self.get_datetime(),
                             self.trading_client.current_data)

    @staticmethod
    def __convert_order_params_for_blotter(limit_price, stop_price, style):
        """
        Helper method for converting deprecated limit_price and stop_price
        arguments into ExecutionStyle instances.

        This function assumes that either style == None or (limit_price,
        stop_price) == (None, None).
        """
        if style:
            assert (limit_price, stop_price) == (None, None)
            return style
        if limit_price and stop_price:
            return StopLimitOrder(limit_price, stop_price)
        if limit_price:
            return LimitOrder(limit_price)
        if stop_price:
            return StopOrder(stop_price)
        else:
            return MarketOrder()

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def order_value(self,
                    asset,
                    value,
                    limit_price=None,
                    stop_price=None,
                    style=None):
        """Place an order by desired value rather than desired number of
        shares.

        Parameters
        ----------
        asset : Asset
            The asset that this order is for.
        value : float
            If the requested asset exists, the requested value is
            divided by its price to imply the number of shares to transact.
            If the Asset being ordered is a Future, the 'value' calculated
            is actually the exposure, as Futures have no 'value'.

            value > 0 :: Buy/Cover
            value < 0 :: Sell/Short
        limit_price : float, optional
            The limit price for the order.
        stop_price : float, optional
            The stop price for the order.
        style : ExecutionStyle
            The execution style for the order.

        Returns
        -------
        order_id : str
            The unique identifier for this order.

        Notes
        -----
        See :func:`zipline.api.order` for more information about
        ``limit_price``, ``stop_price``, and ``style``

        See Also
        --------
        :class:`zipline.finance.execution.ExecutionStyle`
        :func:`zipline.api.order`
        :func:`zipline.api.order_percent`
        """
        if not self._can_order_asset(asset):
            return None

        amount = self._calculate_order_value_amount(asset, value)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)

    @property
    def recorded_vars(self):
        return copy(self._recorded_vars)

    @property
    def portfolio(self):
        return self.updated_portfolio()

    def updated_portfolio(self):
        if self.portfolio_needs_update:
            self.perf_tracker.position_tracker.sync_last_sale_prices(
                self.datetime, self._in_before_trading_start, self.data_portal)
            self._portfolio = \
                self.perf_tracker.get_portfolio(self.performance_needs_update)
            self.portfolio_needs_update = False
            self.performance_needs_update = False
        return self._portfolio

    @property
    def account(self):
        return self.updated_account()

    def updated_account(self):
        if self.account_needs_update:
            self.perf_tracker.position_tracker.sync_last_sale_prices(
                self.datetime, self._in_before_trading_start, self.data_portal)
            self._account = \
                self.perf_tracker.get_account(self.performance_needs_update)

            self.account_needs_update = False
            self.performance_needs_update = False
        return self._account

    def set_logger(self, logger):
        self.logger = logger

    def on_dt_changed(self, dt):
        """
        Callback triggered by the simulation loop whenever the current dt
        changes.

        Any logic that should happen exactly once at the start of each datetime
        group should happen here.
        """
        self.datetime = dt
        self.perf_tracker.set_date(dt)
        self.blotter.set_date(dt)

        self.portfolio_needs_update = True
        self.account_needs_update = True
        self.performance_needs_update = True

    @api_method
    @preprocess(tz=coerce_string(pytz.timezone))
    @expect_types(tz=optional(tzinfo))
    def get_datetime(self, tz=None):
        """
        Returns the current simulation datetime.

        Parameters
        ----------
        tz : tzinfo or str, optional
            The timezone to return the datetime in. This defaults to utc.

        Returns
        -------
        dt : datetime
            The current simulation datetime converted to ``tz``.
        """
        dt = self.datetime
        assert dt.tzinfo == pytz.utc, "Algorithm should have a utc datetime"
        if tz is not None:
            dt = dt.astimezone(tz)
        return dt

    @api_method
    def set_slippage(self, slippage):
        """Set the slippage model for the simulation.

        Parameters
        ----------
        slippage : SlippageModel
            The slippage model to use.

        See Also
        --------
        :class:`zipline.finance.slippage.SlippageModel`
        """
        if not isinstance(slippage, SlippageModel):
            raise UnsupportedSlippageModel()
        if self.initialized:
            raise SetSlippagePostInit()
        self.blotter.slippage_func = slippage

    @api_method
    def set_commission(self, commission):
        """Sets the commission model for the simulation.

        Parameters
        ----------
        commission : CommissionModel
            The commission model to use.

        See Also
        --------
        :class:`zipline.finance.commission.PerShare`
        :class:`zipline.finance.commission.PerTrade`
        :class:`zipline.finance.commission.PerDollar`
        """
        if not isinstance(commission, CommissionModel):
            raise UnsupportedCommissionModel()

        if self.initialized:
            raise SetCommissionPostInit()

        self.blotter.commission = commission

    @api_method
    def set_cancel_policy(self, cancel_policy):
        """Sets the order cancellation policy for the simulation.

        Parameters
        ----------
        cancel_policy : CancelPolicy
            The cancellation policy to use.

        See Also
        --------
        :class:`zipline.api.EODCancel`
        :class:`zipline.api.NeverCancel`
        """
        if not isinstance(cancel_policy, CancelPolicy):
            raise UnsupportedCancelPolicy()

        if self.initialized:
            raise SetCancelPolicyPostInit()

        self.blotter.cancel_policy = cancel_policy

    @api_method
    def set_symbol_lookup_date(self, dt):
        """Set the date for which symbols will be resolved to their assets
        (symbols may map to different firms or underlying assets at
        different times)

        Parameters
        ----------
        dt : datetime
            The new symbol lookup date.
        """
        try:
            self._symbol_lookup_date = pd.Timestamp(dt, tz='UTC')
        except ValueError:
            raise UnsupportedDatetimeFormat(input=dt,
                                            method='set_symbol_lookup_date')

    # Remain backwards compatibility
    @property
    def data_frequency(self):
        return self.sim_params.data_frequency

    @data_frequency.setter
    def data_frequency(self, value):
        assert value in ('daily', 'minute')
        self.sim_params.data_frequency = value

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def order_percent(self,
                      asset,
                      percent,
                      limit_price=None,
                      stop_price=None,
                      style=None):
        """Place an order in the specified asset corresponding to the given
        percent of the current portfolio value.

        Parameters
        ----------
        asset : Asset
            The asset that this order is for.
        percent : float
            The percentage of the porfolio value to allocate to ``asset``.
            This is specified as a decimal, for example: 0.50 means 50%.
        limit_price : float, optional
            The limit price for the order.
        stop_price : float, optional
            The stop price for the order.
        style : ExecutionStyle
            The execution style for the order.

        Returns
        -------
        order_id : str
            The unique identifier for this order.

        Notes
        -----
        See :func:`zipline.api.order` for more information about
        ``limit_price``, ``stop_price``, and ``style``

        See Also
        --------
        :class:`zipline.finance.execution.ExecutionStyle`
        :func:`zipline.api.order`
        :func:`zipline.api.order_value`
        """
        if not self._can_order_asset(asset):
            return None

        amount = self._calculate_order_percent_amount(asset, percent)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)

    def _calculate_order_percent_amount(self, asset, percent):
        value = self.portfolio.portfolio_value * percent
        return self._calculate_order_value_amount(asset, value)

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def order_target(self,
                     asset,
                     target,
                     limit_price=None,
                     stop_price=None,
                     style=None):
        """Place an order to adjust a position to a target number of shares. If
        the position doesn't already exist, this is equivalent to placing a new
        order. If the position does exist, this is equivalent to placing an
        order for the difference between the target number of shares and the
        current number of shares.

        Parameters
        ----------
        asset : Asset
            The asset that this order is for.
        target : int
            The desired number of shares of ``asset``.
        limit_price : float, optional
            The limit price for the order.
        stop_price : float, optional
            The stop price for the order.
        style : ExecutionStyle
            The execution style for the order.

        Returns
        -------
        order_id : str
            The unique identifier for this order.


        Notes
        -----
        ``order_target`` does not take into account any open orders. For
        example:

        .. code-block:: python

           order_target(sid(0), 10)
           order_target(sid(0), 10)

        This code will result in 20 shares of ``sid(0)`` because the first
        call to ``order_target`` will not have been filled when the second
        ``order_target`` call is made.

        See :func:`zipline.api.order` for more information about
        ``limit_price``, ``stop_price``, and ``style``

        See Also
        --------
        :class:`zipline.finance.execution.ExecutionStyle`
        :func:`zipline.api.order`
        :func:`zipline.api.order_target_percent`
        :func:`zipline.api.order_target_value`
        """
        if not self._can_order_asset(asset):
            return None

        amount = self._calculate_order_target_amount(asset, target)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)

    def _calculate_order_target_amount(self, asset, target):
        if asset in self.portfolio.positions:
            current_position = self.portfolio.positions[asset].amount
            target -= current_position

        return target

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def order_target_value(self,
                           asset,
                           target,
                           limit_price=None,
                           stop_price=None,
                           style=None):
        """Place an order to adjust a position to a target value. If
        the position doesn't already exist, this is equivalent to placing a new
        order. If the position does exist, this is equivalent to placing an
        order for the difference between the target value and the
        current value.
        If the Asset being ordered is a Future, the 'target value' calculated
        is actually the target exposure, as Futures have no 'value'.

        Parameters
        ----------
        asset : Asset
            The asset that this order is for.
        target : float
            The desired total value of ``asset``.
        limit_price : float, optional
            The limit price for the order.
        stop_price : float, optional
            The stop price for the order.
        style : ExecutionStyle
            The execution style for the order.

        Returns
        -------
        order_id : str
            The unique identifier for this order.

        Notes
        -----
        ``order_target_value`` does not take into account any open orders. For
        example:

        .. code-block:: python

           order_target_value(sid(0), 10)
           order_target_value(sid(0), 10)

        This code will result in 20 dollars of ``sid(0)`` because the first
        call to ``order_target_value`` will not have been filled when the
        second ``order_target_value`` call is made.

        See :func:`zipline.api.order` for more information about
        ``limit_price``, ``stop_price``, and ``style``

        See Also
        --------
        :class:`zipline.finance.execution.ExecutionStyle`
        :func:`zipline.api.order`
        :func:`zipline.api.order_target`
        :func:`zipline.api.order_target_percent`
        """
        if not self._can_order_asset(asset):
            return None

        target_amount = self._calculate_order_value_amount(asset, target)
        amount = self._calculate_order_target_amount(asset, target_amount)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def order_target_percent(self, asset, target,
                             limit_price=None, stop_price=None, style=None):
        """Place an order to adjust a position to a target percent of the
        current portfolio value. If the position doesn't already exist, this is
        equivalent to placing a new order. If the position does exist, this is
        equivalent to placing an order for the difference between the target
        percent and the current percent.

        Parameters
        ----------
        asset : Asset
            The asset that this order is for.
        target : float
            The desired percentage of the porfolio value to allocate to
            ``asset``. This is specified as a decimal, for example:
            0.50 means 50%.
        limit_price : float, optional
            The limit price for the order.
        stop_price : float, optional
            The stop price for the order.
        style : ExecutionStyle
            The execution style for the order.

        Returns
        -------
        order_id : str
            The unique identifier for this order.

        Notes
        -----
        ``order_target_value`` does not take into account any open orders. For
        example:

        .. code-block:: python

           order_target_percent(sid(0), 10)
           order_target_percent(sid(0), 10)

        This code will result in 20% of the portfolio being allocated to sid(0)
        because the first call to ``order_target_percent`` will not have been
        filled when the second ``order_target_percent`` call is made.

        See :func:`zipline.api.order` for more information about
        ``limit_price``, ``stop_price``, and ``style``

        See Also
        --------
        :class:`zipline.finance.execution.ExecutionStyle`
        :func:`zipline.api.order`
        :func:`zipline.api.order_target`
        :func:`zipline.api.order_target_value`
        """
        if not self._can_order_asset(asset):
            return None

        amount = self._calculate_order_target_percent_amount(asset, target)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)

    def _calculate_order_target_percent_amount(self, asset, target):
        target_amount = self._calculate_order_percent_amount(asset, target)
        return self._calculate_order_target_amount(asset, target_amount)

    @api_method
    @disallowed_in_before_trading_start(OrderInBeforeTradingStart())
    def batch_order_target_percent(self, weights):
        """Place orders towards a given portfolio of weights.

        Parameters
        ----------
        weights : collections.Mapping[Asset -> float]

        Returns
        -------
        order_ids : pd.Series[Asset -> str]
            The unique identifiers for the orders that were placed.

        See Also
        --------
        :func:`zipline.api.order_target_percent`
        """
        order_args = OrderedDict()
        for asset, target in iteritems(weights):
            if self._can_order_asset(asset):
                amount = self._calculate_order_target_percent_amount(
                    asset, target,
                )
                amount, style = self._calculate_order(asset, amount)
                order_args[asset] = (asset, amount, style)

        order_ids = self.blotter.batch_order(viewvalues(order_args))
        order_ids = pd.Series(data=order_ids, index=order_args)
        return order_ids[~order_ids.isnull()]

    @error_keywords(sid='Keyword argument `sid` is no longer supported for '
                        'get_open_orders. Use `asset` instead.')
    @api_method
    def get_open_orders(self, asset=None):
        """Retrieve all of the current open orders.

        Parameters
        ----------
        asset : Asset
            If passed and not None, return only the open orders for the given
            asset instead of all open orders.

        Returns
        -------
        open_orders : dict[list[Order]] or list[Order]
            If no asset is passed this will return a dict mapping Assets
            to a list containing all the open orders for the asset.
            If an asset is passed then this will return a list of the open
            orders for this asset.
        """
        if asset is None:
            return {
                key: [order.to_api_obj() for order in orders]
                for key, orders in iteritems(self.blotter.open_orders)
                if orders
            }
        if asset in self.blotter.open_orders:
            orders = self.blotter.open_orders[asset]
            return [order.to_api_obj() for order in orders]
        return []

    @api_method
    def get_order(self, order_id):
        """Lookup an order based on the order id returned from one of the
        order functions.

        Parameters
        ----------
        order_id : str
            The unique identifier for the order.

        Returns
        -------
        order : Order
            The order object.
        """
        if order_id in self.blotter.orders:
            return self.blotter.orders[order_id].to_api_obj()

    @api_method
    def cancel_order(self, order_param):
        """Cancel an open order.

        Parameters
        ----------
        order_param : str or Order
            The order_id or order object to cancel.
        """
        order_id = order_param
        if isinstance(order_param, zipline.protocol.Order):
            order_id = order_param.id

        self.blotter.cancel(order_id)

    @api_method
    @require_initialized(HistoryInInitialize())
    def history(self, bar_count, frequency, field, ffill=True):
        """DEPRECATED: use ``data.history`` instead.
        """
        warnings.warn(
            "The `history` method is deprecated.  Use `data.history` instead.",
            category=ZiplineDeprecationWarning,
            stacklevel=4
        )

        return self.get_history_window(
            bar_count,
            frequency,
            self._calculate_universe(),
            field,
            ffill
        )

    def get_history_window(self, bar_count, frequency, assets, field, ffill):
        if not self._in_before_trading_start:
            return self.data_portal.get_history_window(
                assets,
                self.datetime,
                bar_count,
                frequency,
                field,
                ffill,
            )
        else:
            # If we are in before_trading_start, we need to get the window
            # as of the previous market minute
            adjusted_dt = \
                self.trading_calendar.previous_minute(
                    self.datetime
                )

            window = self.data_portal.get_history_window(
                assets,
                adjusted_dt,
                bar_count,
                frequency,
                field,
                ffill,
            )

            # Get the adjustments between the last market minute and the
            # current before_trading_start dt and apply to the window
            adjs = self.data_portal.get_adjustments(
                assets,
                field,
                adjusted_dt,
                self.datetime
            )
            window = window * adjs

            return window

    ####################
    # Account Controls #
    ####################

    def register_account_control(self, control):
        """
        Register a new AccountControl to be checked on each bar.
        """
        if self.initialized:
            raise RegisterAccountControlPostInit()
        self.account_controls.append(control)

    def validate_account_controls(self):
        for control in self.account_controls:
            control.validate(self.updated_portfolio(),
                             self.updated_account(),
                             self.get_datetime(),
                             self.trading_client.current_data)

    @api_method
    def set_max_leverage(self, max_leverage):
        """Set a limit on the maximum leverage of the algorithm.

        Parameters
        ----------
        max_leverage : float
            The maximum leverage for the algorithm. If not provided there will
            be no maximum.
        """
        control = MaxLeverage(max_leverage)
        self.register_account_control(control)

    ####################
    # Trading Controls #
    ####################

    def register_trading_control(self, control):
        """
        Register a new TradingControl to be checked prior to order calls.
        """
        if self.initialized:
            raise RegisterTradingControlPostInit()
        self.trading_controls.append(control)

    @api_method
    def set_max_position_size(self,
                              asset=None,
                              max_shares=None,
                              max_notional=None,
                              on_error='fail'):
        """Set a limit on the number of shares and/or dollar value held for the
        given sid. Limits are treated as absolute values and are enforced at
        the time that the algo attempts to place an order for sid. This means
        that it's possible to end up with more than the max number of shares
        due to splits/dividends, and more than the max notional due to price
        improvement.

        If an algorithm attempts to place an order that would result in
        increasing the absolute value of shares/dollar value exceeding one of
        these limits, raise a TradingControlException.

        Parameters
        ----------
        asset : Asset, optional
            If provided, this sets the guard only on positions in the given
            asset.
        max_shares : int, optional
            The maximum number of shares to hold for an asset.
        max_notional : float, optional
            The maximum value to hold for an asset.
        """
        control = MaxPositionSize(asset=asset,
                                  max_shares=max_shares,
                                  max_notional=max_notional,
                                  on_error=on_error)
        self.register_trading_control(control)

    @api_method
    def set_max_order_size(self,
                           asset=None,
                           max_shares=None,
                           max_notional=None,
                           on_error='fail'):
        """Set a limit on the number of shares and/or dollar value of any single
        order placed for sid.  Limits are treated as absolute values and are
        enforced at the time that the algo attempts to place an order for sid.

        If an algorithm attempts to place an order that would result in
        exceeding one of these limits, raise a TradingControlException.

        Parameters
        ----------
        asset : Asset, optional
            If provided, this sets the guard only on positions in the given
            asset.
        max_shares : int, optional
            The maximum number of shares that can be ordered at one time.
        max_notional : float, optional
            The maximum value that can be ordered at one time.
        """
        control = MaxOrderSize(asset=asset,
                               max_shares=max_shares,
                               max_notional=max_notional,
                               on_error=on_error)
        self.register_trading_control(control)

    @api_method
    def set_max_order_count(self, max_count, on_error='fail'):
        """Set a limit on the number of orders that can be placed in a single
        day.

        Parameters
        ----------
        max_count : int
            The maximum number of orders that can be placed on any single day.
        """
        control = MaxOrderCount(on_error, max_count)
        self.register_trading_control(control)

    @api_method
    def set_do_not_order_list(self, restricted_list, on_error='fail'):
        """Set a restriction on which assets can be ordered.

        Parameters
        ----------
        restricted_list : container[Asset], SecurityList
            The assets that cannot be ordered.
        """
        if isinstance(restricted_list, SecurityList):
            warnings.warn(
                "`set_do_not_order_list(security_lists.leveraged_etf_list)` "
                "is deprecated. Use `set_asset_restrictions("
                "security_lists.restrict_leveraged_etfs)` instead.",
                category=ZiplineDeprecationWarning,
                stacklevel=2
            )
            restrictions = SecurityListRestrictions(restricted_list)
        else:
            warnings.warn(
                "`set_do_not_order_list(container_of_assets)` is deprecated. "
                "Create a zipline.finance.asset_restrictions."
                "StaticRestrictions object with a container of assets and use "
                "`set_asset_restrictions(StaticRestrictions("
                "container_of_assets))` instead.",
                category=ZiplineDeprecationWarning,
                stacklevel=2
            )
            restrictions = StaticRestrictions(restricted_list)

        self.set_asset_restrictions(restrictions, on_error)

    @api_method
    @expect_types(
        restrictions=Restrictions,
        on_error=str,
    )
    def set_asset_restrictions(self, restrictions, on_error='fail'):
        """Set a restriction on which assets can be ordered.

        Parameters
        ----------
        restricted_list : Restrictions
            An object providing information about restricted assets.

        See Also
        --------
        zipline.finance.asset_restrictions.Restrictions
        """
        control = RestrictedListOrder(on_error, restrictions)
        self.register_trading_control(control)
        self.restrictions |= restrictions

    @api_method
    def set_long_only(self, on_error='fail'):
        """Set a rule specifying that this algorithm cannot take short
        positions.
        """
        self.register_trading_control(LongOnly(on_error))

    ##############
    # Pipeline API
    ##############
    @api_method
    @require_not_initialized(AttachPipelineAfterInitialize())
    @expect_types(
        pipeline=Pipeline,
        name=string_types,
        chunks=(int, Iterable, type(None)),
    )
    def attach_pipeline(self, pipeline, name, chunks=None):
        """Register a pipeline to be computed at the start of each day.

        Parameters
        ----------
        pipeline : Pipeline
            The pipeline to have computed.
        name : str
            The name of the pipeline.
        chunks : int or iterator, optional
            The number of days to compute pipeline results for. Increasing
            this number will make it longer to get the first results but
            may improve the total runtime of the simulation. If an iterator
            is passed, we will run in chunks based on values of the itereator.

        Returns
        -------
        pipeline : Pipeline
            Returns the pipeline that was attached unchanged.

        See Also
        --------
        :func:`zipline.api.pipeline_output`
        """
        if self._pipelines:
            raise NotImplementedError("Multiple pipelines are not supported.")
        if chunks is None:
            # Make the first chunk smaller to get more immediate results:
            # (one week, then every half year)
            chunks = chain([5], repeat(126))
        elif isinstance(chunks, int):
            chunks = repeat(chunks)
        self._pipelines[name] = pipeline, iter(chunks)

        # Return the pipeline to allow expressions like
        # p = attach_pipeline(Pipeline(), 'name')
        return pipeline

    @api_method
    @require_initialized(PipelineOutputDuringInitialize())
    def pipeline_output(self, name):
        """Get the results of the pipeline that was attached with the name:
        ``name``.

        Parameters
        ----------
        name : str
            Name of the pipeline for which results are requested.

        Returns
        -------
        results : pd.DataFrame
            DataFrame containing the results of the requested pipeline for
            the current simulation date.

        Raises
        ------
        NoSuchPipeline
            Raised when no pipeline with the name `name` has been registered.

        See Also
        --------
        :func:`zipline.api.attach_pipeline`
        :meth:`zipline.pipeline.engine.PipelineEngine.run_pipeline`
        """
        # NOTE: We don't currently support multiple pipelines, but we plan to
        # in the future.
        try:
            p, chunks = self._pipelines[name]
        except KeyError:
            raise NoSuchPipeline(
                name=name,
                valid=list(self._pipelines.keys()),
            )
        return self._pipeline_output(p, chunks)

    def _pipeline_output(self, pipeline, chunks):
        """
        Internal implementation of `pipeline_output`.
        """
        today = normalize_date(self.get_datetime())
        data = NO_DATA = object()
        try:
            data = self._pipeline_cache.unwrap(today)
        except Expired:
            # We can't handle the exception in this block because in Python 3
            # sys.exc_info isn't cleared until we leave the block.  See note
            # below for why we need to clear exc_info.
            pass

        if data is NO_DATA:
            # Try to deterministically garbage collect the previous result by
            # removing any references to it. There are at least three sources
            # of references:

            # 1. self._pipeline_cache holds a reference.
            # 2. The dataframe itself holds a reference via cached .iloc/.loc
            #    accessors.
            # 3. The traceback held in sys.exc_info includes stack frames in
            #    which self._pipeline_cache is a local variable.

            # We remove the above sources of references in reverse order:

            # 3. Clear the traceback.  This is no-op in Python 3.
            exc_clear()

            # 2. Clear the .loc/.iloc caches.
            clear_dataframe_indexer_caches(
                self._pipeline_cache._unsafe_get_value()
            )

            # 1. Clear the reference to self._pipeline_cache.
            self._pipeline_cache = None

            # Calculate the next block.
            data, valid_until = self._run_pipeline(
                pipeline, today, next(chunks),
            )
            self._pipeline_cache = CachedObject(data, valid_until)

        # Now that we have a cached result, try to return the data for today.
        try:
            return data.loc[today]
        except KeyError:
            # This happens if no assets passed the pipeline screen on a given
            # day.
            return pd.DataFrame(index=[], columns=data.columns)

    def _run_pipeline(self, pipeline, start_session, chunksize):
        """
        Compute `pipeline`, providing values for at least `start_date`.

        Produces a DataFrame containing data for days between `start_date` and
        `end_date`, where `end_date` is defined by:

            `end_date = min(start_date + chunksize trading days,
                            simulation_end)`

        Returns
        -------
        (data, valid_until) : tuple (pd.DataFrame, pd.Timestamp)

        See Also
        --------
        PipelineEngine.run_pipeline
        """
        sessions = self.trading_calendar.all_sessions

        # Load data starting from the previous trading day...
        start_date_loc = sessions.get_loc(start_session)

        # ...continuing until either the day before the simulation end, or
        # until chunksize days of data have been loaded.
        sim_end_session = self.sim_params.end_session

        end_loc = min(
            start_date_loc + chunksize,
            sessions.get_loc(sim_end_session)
        )

        end_session = sessions[end_loc]

        return \
            self.engine.run_pipeline(pipeline, start_session, end_session), \
            end_session

    ##################
    # End Pipeline API
    ##################

    @classmethod
    def all_api_methods(cls):
        """
        Return a list of all the TradingAlgorithm API methods.
        """
        return [
            fn for fn in itervalues(vars(cls))
            if getattr(fn, 'is_api_method', False)
        ]