#!/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)