item_21.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 sort_priority(values, group):
    def helper(x):
        if x in group:
            return (0, x)
        return (1, x)
    values.sort(key=helper)


# Example 2
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
group = {2, 3, 5, 7}
sort_priority(numbers, group)
print(numbers)


# Example 3
def sort_priority2(numbers, group):
    found = False
    def helper(x):
        if x in group:
            found = True  # Seems simple
            return (0, x)
        return (1, x)
    numbers.sort(key=helper)
    return found


# Example 4
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
found = sort_priority2(numbers, group)
print('Found:', found)
print(numbers)


# Example 5
try:
    foo = does_not_exist * 5
except:
    logging.exception('Expected')
else:
    assert False


# Example 6
def sort_priority2(numbers, group):
    found = False         # Scope: 'sort_priority2'
    def helper(x):
        if x in group:
            found = True  # Scope: 'helper' -- Bad!
            return (0, x)
        return (1, x)
    numbers.sort(key=helper)
    return found


# Example 7
def sort_priority3(numbers, group):
    found = False
    def helper(x):
        nonlocal found  # Added
        if x in group:
            found = True
            return (0, x)
        return (1, x)
    numbers.sort(key=helper)
    return found


# Example 8
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
found = sort_priority3(numbers, group)
assert found
assert numbers == [2, 3, 5, 7, 1, 4, 6, 8]


# Example 9
numbers = [8, 3, 1, 2, 5, 4, 7, 6]
class Sorter:
    def __init__(self, group):
        self.group = group
        self.found = False

    def __call__(self, x):
        if x in self.group:
            self.found = True
            return (0, x)
        return (1, x)

sorter = Sorter(group)
numbers.sort(key=sorter)
assert sorter.found is True
assert numbers == [2, 3, 5, 7, 1, 4, 6, 8]