#!/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)