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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

pictures = {}

path = 'profile_1234.png'

with open(path, 'wb') as f:

f.write(b'image data here 1234')

if (handle := pictures.get(path)) is None:

try:

handle = open(path, 'a+b')

except OSError:

print(f'Failed to open path {path}')

raise

else:

pictures[path] = handle

handle.seek(0)

image_data = handle.read()

print(pictures)

print(image_data)

# Example 2

# Examples using in and KeyError

pictures = {}

path = 'profile_9991.png'

with open(path, 'wb') as f:

f.write(b'image data here 9991')

if path in pictures:

handle = pictures[path]

else:

try:

handle = open(path, 'a+b')

except OSError:

print(f'Failed to open path {path}')

raise

else:

pictures[path] = handle

handle.seek(0)

image_data = handle.read()

print(pictures)

print(image_data)

pictures = {}

path = 'profile_9922.png'

with open(path, 'wb') as f:

f.write(b'image data here 9991')

try:

handle = pictures[path]

except KeyError:

try:

handle = open(path, 'a+b')

except OSError:

print(f'Failed to open path {path}')

raise

else:

pictures[path] = handle

handle.seek(0)

image_data = handle.read()

print(pictures)

print(image_data)

# Example 3

pictures = {}

path = 'profile_9239.png'

with open(path, 'wb') as f:

f.write(b'image data here 9239')

try:

handle = pictures.setdefault(path, open(path, 'a+b'))

except OSError:

print(f'Failed to open path {path}')

raise

else:

handle.seek(0)

image_data = handle.read()

print(pictures)

print(image_data)

# Example 4

try:

path = 'profile_4555.csv'

with open(path, 'wb') as f:

f.write(b'image data here 9239')

from collections import defaultdict

def open_picture(profile_path):

try:

return open(profile_path, 'a+b')

except OSError:

print(f'Failed to open path {profile_path}')

raise

pictures = defaultdict(open_picture)

handle = pictures[path]

handle.seek(0)

image_data = handle.read()

except:

logging.exception('Expected')

else:

assert False

# Example 5

path = 'account_9090.csv'

with open(path, 'wb') as f:

f.write(b'image data here 9090')

def open_picture(profile_path):

try:

return open(profile_path, 'a+b')

except OSError:

print(f'Failed to open path {profile_path}')

raise

class Pictures(dict):

def __missing__(self, key):

value = open_picture(key)

self[key] = value

return value

pictures = Pictures()

handle = pictures[path]

handle.seek(0)

image_data = handle.read()

print(pictures)

print(image_data)