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#!/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

stock = {

'nails': 125,

'screws': 35,

'wingnuts': 8,

'washers': 24,

}

order = ['screws', 'wingnuts', 'clips']

def get_batches(count, size):

return count // size

result = {}

for name in order:

count = stock.get(name, 0)

batches = get_batches(count, 8)

if batches:

result[name] = batches

print(result)

# Example 2

found = {name: get_batches(stock.get(name, 0), 8)

for name in order

if get_batches(stock.get(name, 0), 8)}

print(found)

# Example 3

has_bug = {name: get_batches(stock.get(name, 0), 4)

for name in order

if get_batches(stock.get(name, 0), 8)}

print('Expected:', found)

print('Found: ', has_bug)

# Example 4

found = {name: batches for name in order

if (batches := get_batches(stock.get(name, 0), 8))}

assert found == {'screws': 4, 'wingnuts': 1}, found

# Example 5

try:

result = {name: (tenth := count // 10)

for name, count in stock.items() if tenth > 0}

except:

logging.exception('Expected')

else:

assert False

# Example 6

result = {name: tenth for name, count in stock.items()

if (tenth := count // 10) > 0}

print(result)

# Example 7

half = [(last := count // 2) for count in stock.values()]

print(f'Last item of {half} is {last}')

# Example 8

for count in stock.values(): # Leaks loop variable

pass

print(f'Last item of {list(stock.values())} is {count}')

# Example 9

try:

del count

half = [count // 2 for count in stock.values()]

print(half) # Works

print(count) # Exception because loop variable didn't leak

except:

logging.exception('Expected')

else:

assert False

# Example 10

found = ((name, batches) for name in order

if (batches := get_batches(stock.get(name, 0), 8)))

print(next(found))

print(next(found))