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item_03.py
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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
a = b'h\x65llo'
print(list(a))
print(a)
# Example 2
a = 'a\u0300 propos'
print(list(a))
print(a)
# Example 3
def to_str(bytes_or_str):
if isinstance(bytes_or_str, bytes):
value = bytes_or_str.decode('utf-8')
else:
value = bytes_or_str
return value # Instance of str
print(repr(to_str(b'foo')))
print(repr(to_str('bar')))
# Example 4
def to_bytes(bytes_or_str):
if isinstance(bytes_or_str, str):
value = bytes_or_str.encode('utf-8')
else:
value = bytes_or_str
return value # Instance of bytes
print(repr(to_bytes(b'foo')))
print(repr(to_bytes('bar')))
# Example 5
print(b'one' + b'two')
print('one' + 'two')
# Example 6
try:
b'one' + 'two' #string cocatenate problrm byte and string
except:
logging.exception('Expected')
else:
assert False
# Example 7
try:
'one' + b'two'
except:
logging.exception('Expected')
else:
assert False
# Example 8
assert b'red' > b'blue'
assert 'red' > 'blue'
# Example 9
try:
assert 'red' > b'blue' #compare byte with string problem
except:
logging.exception('Expected')
else:
assert False
# Example 10
try:
assert b'blue' < 'red' #compare byte to string problem
except:
logging.exception('Expected')
else:
assert False
# Example 11
print(b'foo' == 'foo') #compare byte with string error
# Example 12
print(b'red %s' % b'blue')
print('red %s' % 'blue')
# Example 13
try:
print(b'red %s' % 'blue') #cannot combine byte wit string
except:
logging.exception('Expected')
else:
assert False
# Example 14
print('red %s' % b'blue') #combine string with byte works
# Example 15
try:
with open('data.bin', 'w') as f: #'w' expects sring as write value
f.write(b'\xf1\xf2\xf3\xf4\xf5')
except:
logging.exception('Expected')
else:
assert False
# Example 16
with open('data.bin', 'wb') as f: #use wb instead of w for bytes coded
f.write(b'\xf1\xf2\xf3\xf4\xf5')
# Example 17
try:
# Silently force UTF-8 here to make sure this test fails on
# all platforms. cp1252 considers these bytes valid on Windows.
real_open = open
def open(*args, **kwargs):
kwargs['encoding'] = 'utf-8'
return real_open(*args, **kwargs)
with open('data.bin', 'r') as f: #created new function open read only utf-8
data = f.read()
except:
logging.exception('Expected')
else:
assert False
# Example 18
# Restore the overloaded open above.
open = real_open #set default setting open back
with open('data.bin', 'rb') as f:
data = f.read()
assert data == b'\xf1\xf2\xf3\xf4\xf5'
# Example 19
with open('data.bin', 'r', encoding='cp1252') as f: #can read non-utf 8 also
data = f.read()
assert data == 'ñòóôõ'
with open('data.bin', 'r') as f: #can read non-utf 8 also
data = f.read()