#!/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 a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] print('Middle two: ', a[3:5]) print('All but ends:', a[1:7]) # Example 2 assert a[:5] == a[0:5] # Example 3 assert a[5:] == a[5:len(a)] # Example 4 print(a[:]) print(a[:5]) print(a[:-1]) print(a[4:]) print(a[-3:]) print(a[2:5]) print(a[2:-1]) print(a[-3:-1]) # Example 5 a[:] # ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] a[:5] # ['a', 'b', 'c', 'd', 'e'] a[:-1] # ['a', 'b', 'c', 'd', 'e', 'f', 'g'] a[4:] # ['e', 'f', 'g', 'h'] a[-3:] # ['f', 'g', 'h'] a[2:5] # ['c', 'd', 'e'] a[2:-1] # ['c', 'd', 'e', 'f', 'g'] a[-3:-1] # ['f', 'g'] # Example 6 first_twenty_items = a[:20] last_twenty_items = a[-20:] # Example 7 try: a[20] except: logging.exception('Expected') else: assert False # Example 8 b = a[3:] print('Before: ', b) b[1] = 99 print('After: ', b) print('No change:', a) # Example 9 print('Before ', a) a[2:7] = [99, 22, 14] print('After ', a) # Example 10 print('Before ', a) a[2:3] = [47, 11] print('After ', a) # Example 11 b = a[:] assert b == a and b is not a # Example 12 b = a print('Before a', a) print('Before b', b) a[:] = [101, 102, 103] assert a is b # Still the same list object print('After a ', a) # Now has different contents print('After b ', b) # Same list, so same contents as a