#!/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 try: def subtract(a, b): return a - b subtract(10, '5') except: logging.exception('Expected') else: assert False # Example 3 try: def concat(a, b): return a + b concat('first', b'second') except: logging.exception('Expected') else: assert False # Example 5 class Counter: def __init__(self): self.value = 0 def add(self, offset): value += offset def get(self) -> int: self.value # Example 6 try: counter = Counter() counter.add(5) except: logging.exception('Expected') else: assert False # Example 7 try: counter = Counter() found = counter.get() assert found == 0, found except: logging.exception('Expected') else: assert False # Example 9 try: def combine(func, values): assert len(values) > 0 result = values[0] for next_value in values[1:]: result = func(result, next_value) return result def add(x, y): return x + y inputs = [1, 2, 3, 4j] result = combine(add, inputs) assert result == 10, result # Fails except: logging.exception('Expected') else: assert False # Example 11 try: def get_or_default(value, default): if value is not None: return value return value found = get_or_default(3, 5) assert found == 3 found = get_or_default(None, 5) assert found == 5, found # Fails except: logging.exception('Expected') else: assert False # Example 13 class FirstClass: def __init__(self, value): self.value = value class SecondClass: def __init__(self, value): self.value = value second = SecondClass(5) first = FirstClass(second) del FirstClass del SecondClass # Example 15 try: class FirstClass: def __init__(self, value: SecondClass) -> None: # Breaks self.value = value class SecondClass: def __init__(self, value: int) -> None: self.value = value second = SecondClass(5) first = FirstClass(second) except: logging.exception('Expected') else: assert False # Example 16 class FirstClass: def __init__(self, value: 'SecondClass') -> None: # OK self.value = value class SecondClass: def __init__(self, value: int) -> None: self.value = value second = SecondClass(5) first = FirstClass(second)