effectivepython/example_code/item_87.py at master · sharc007/effectivepython · GitHub

History

executable file

189 lines (151 loc) · 4.48 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

#!/usr/bin/env PYTHONHASHSEED=1234 python3

# 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

# my_module.py

def determine_weight(volume, density):

if density <= 0:

raise ValueError('Density must be positive')

try:

determine_weight(1, 0)

except ValueError:

pass

else:

assert False

# Example 2

# my_module.py

class Error(Exception):

"""Base-class for all exceptions raised by this module."""

class InvalidDensityError(Error):

"""There was a problem with a provided density value."""

class InvalidVolumeError(Error):

"""There was a problem with the provided weight value."""

def determine_weight(volume, density):

if density < 0:

raise InvalidDensityError('Density must be positive')

if volume < 0:

raise InvalidVolumeError('Volume must be positive')

if volume == 0:

density / volume

# Example 3

class my_module:

Error = Error

InvalidDensityError = InvalidDensityError

@staticmethod

def determine_weight(volume, density):

if density < 0:

raise InvalidDensityError('Density must be positive')

if volume < 0:

raise InvalidVolumeError('Volume must be positive')

if volume == 0:

density / volume

try:

weight = my_module.determine_weight(1, -1)

except my_module.Error:

logging.exception('Unexpected error')

else:

assert False

# Example 4

SENTINEL = object()

weight = SENTINEL

try:

weight = my_module.determine_weight(-1, 1)

except my_module.InvalidDensityError:

weight = 0

except my_module.Error:

logging.exception('Bug in the calling code')

else:

assert False

assert weight is SENTINEL

# Example 5

try:

weight = SENTINEL

try:

weight = my_module.determine_weight(0, 1)

except my_module.InvalidDensityError:

weight = 0

except my_module.Error:

logging.exception('Bug in the calling code')

except Exception:

logging.exception('Bug in the API code!')

raise # Re-raise exception to the caller

else:

assert False

assert weight == 0

except:

logging.exception('Expected')

else:

assert False

# Example 6

# my_module.py

class NegativeDensityError(InvalidDensityError):

"""A provided density value was negative."""

def determine_weight(volume, density):

if density < 0:

raise NegativeDensityError('Density must be positive')

# Example 7

try:

my_module.NegativeDensityError = NegativeDensityError

my_module.determine_weight = determine_weight

try:

weight = my_module.determine_weight(1, -1)

except my_module.NegativeDensityError:

raise ValueError('Must supply non-negative density')

except my_module.InvalidDensityError:

weight = 0

except my_module.Error:

logging.exception('Bug in the calling code')

except Exception:

logging.exception('Bug in the API code!')

raise

else:

assert False

except:

logging.exception('Expected')

else:

assert False

# Example 8

# my_module.py

class Error(Exception):

"""Base-class for all exceptions raised by this module."""

class WeightError(Error):

"""Base-class for weight calculation errors."""

class VolumeError(Error):

"""Base-class for volume calculation errors."""

class DensityError(Error):

"""Base-class for density calculation errors."""

effectivepython/example_code/item_87.py at master · sharc007/effectivepython · GitHub

Expand file tree

Breadcrumbs

item_87.py

Latest commit

History

Breadcrumbs

item_87.py

File metadata and controls