#!/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]