item_33.py

#!/usr/bin/env PYTHONHASHSEED=1234 python3

# Copyright 2014-2019 Brett Slatkin, Pearson Education 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.

# Reproduce book environment
import random
random.seed(1234)

import logging
from pprint import pprint
from sys import stdout as STDOUT

# Write all output to a temporary directory
import atexit
import gc
import io
import os
import tempfile

TEST_DIR = tempfile.TemporaryDirectory()
atexit.register(TEST_DIR.cleanup)

# Make sure Windows processes exit cleanly
OLD_CWD = os.getcwd()
atexit.register(lambda: os.chdir(OLD_CWD))
os.chdir(TEST_DIR.name)

def close_open_files():
    everything = gc.get_objects()
    for obj in everything:
        if isinstance(obj, io.IOBase):
            obj.close()

atexit.register(close_open_files)


# Example 1
def move(period, speed):
    for _ in range(period):
        yield speed

def pause(delay):
    for _ in range(delay):
        yield 0


# Example 2
def animate():
    for delta in move(4, 5.0):
        yield delta
    for delta in pause(3):
        yield delta
    for delta in move(2, 3.0):
        yield delta


# Example 3
def render(delta):
    print(f'Delta: {delta:.1f}')
    # Move the images onscreen

def run(func):
    for delta in func():
        render(delta)

run(animate)


# Example 4
def animate_composed():
    yield from move(4, 5.0)
    yield from pause(3)
    yield from move(2, 3.0)

run(animate_composed)


# Example 5
import timeit

def child():
    for i in range(1_000_000):
        yield i

def slow():
    for i in child():
        yield i

def fast():
    yield from child()

baseline = timeit.timeit(
    stmt='for _ in slow(): pass',
    globals=globals(),
    number=50)
print(f'Manual nesting {baseline:.2f}s')

comparison = timeit.timeit(
    stmt='for _ in fast(): pass',
    globals=globals(),
    number=50)
print(f'Composed nesting {comparison:.2f}s')

reduction = -(comparison - baseline) / baseline
print(f'{reduction:.1%} less time')