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#!/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 careful_divide(a, b):

try:

return a / b

except ZeroDivisionError:

return None

assert careful_divide(4, 2) == 2

assert careful_divide(0, 1) == 0

assert careful_divide(3, 6) == 0.5

assert careful_divide(1, 0) == None

# Example 2

x, y = 1, 0

result = careful_divide(x, y)

if result is None:

print('Invalid inputs')

else:

print('Result is %.1f' % result)

# Example 3

x, y = 0, 5

result = careful_divide(x, y)

if not result:

print('Invalid inputs') # This runs! But shouldn't

else:

assert False

# Example 4

def careful_divide(a, b):

try:

return True, a / b

except ZeroDivisionError:

return False, None

assert careful_divide(4, 2) == (True, 2)

assert careful_divide(0, 1) == (True, 0)

assert careful_divide(3, 6) == (True, 0.5)

assert careful_divide(1, 0) == (False, None)

# Example 5

x, y = 5, 0

success, result = careful_divide(x, y)

if not success:

print('Invalid inputs')

# Example 6

x, y = 5, 0

_, result = careful_divide(x, y)

if not result:

print('Invalid inputs')

# Example 7

def careful_divide(a, b):

try:

return a / b

except ZeroDivisionError as e:

raise ValueError('Invalid inputs')

# Example 8

x, y = 5, 2

try:

result = careful_divide(x, y)

except ValueError:

print('Invalid inputs')

else:

print('Result is %.1f' % result)

# Example 9

def careful_divide(a: float, b: float) -> float:

"""Divides a by b.

Raises:

ValueError: When the inputs cannot be divided.

"""

try:

return a / b

except ZeroDivisionError as e:

raise ValueError('Invalid inputs')

try:

result = careful_divide(1, 0)

assert False

except ValueError:

pass # Expected

assert careful_divide(1, 5) == 0.2