forked from bslatkin/effectivepython
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathitem_18.py
More file actions
executable file
·191 lines (149 loc) · 3.89 KB
/
item_18.py
File metadata and controls
executable file
·191 lines (149 loc) · 3.89 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
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
190
191
#!/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
pictures = {}
path = 'profile_1234.png'
with open(path, 'wb') as f:
f.write(b'image data here 1234')
if (handle := pictures.get(path)) is None:
try:
handle = open(path, 'a+b')
except OSError:
print(f'Failed to open path {path}')
raise
else:
pictures[path] = handle
handle.seek(0)
image_data = handle.read()
print(pictures)
print(image_data)
# Example 2
# Examples using in and KeyError
pictures = {}
path = 'profile_9991.png'
with open(path, 'wb') as f:
f.write(b'image data here 9991')
if path in pictures:
handle = pictures[path]
else:
try:
handle = open(path, 'a+b')
except OSError:
print(f'Failed to open path {path}')
raise
else:
pictures[path] = handle
handle.seek(0)
image_data = handle.read()
print(pictures)
print(image_data)
pictures = {}
path = 'profile_9922.png'
with open(path, 'wb') as f:
f.write(b'image data here 9991')
try:
handle = pictures[path]
except KeyError:
try:
handle = open(path, 'a+b')
except OSError:
print(f'Failed to open path {path}')
raise
else:
pictures[path] = handle
handle.seek(0)
image_data = handle.read()
print(pictures)
print(image_data)
# Example 3
pictures = {}
path = 'profile_9239.png'
with open(path, 'wb') as f:
f.write(b'image data here 9239')
try:
handle = pictures.setdefault(path, open(path, 'a+b'))
except OSError:
print(f'Failed to open path {path}')
raise
else:
handle.seek(0)
image_data = handle.read()
print(pictures)
print(image_data)
# Example 4
try:
path = 'profile_4555.csv'
with open(path, 'wb') as f:
f.write(b'image data here 9239')
from collections import defaultdict
def open_picture(profile_path):
try:
return open(profile_path, 'a+b')
except OSError:
print(f'Failed to open path {profile_path}')
raise
pictures = defaultdict(open_picture)
handle = pictures[path]
handle.seek(0)
image_data = handle.read()
except:
logging.exception('Expected')
else:
assert False
# Example 5
path = 'account_9090.csv'
with open(path, 'wb') as f:
f.write(b'image data here 9090')
def open_picture(profile_path):
try:
return open(profile_path, 'a+b')
except OSError:
print(f'Failed to open path {profile_path}')
raise
class Pictures(dict):
def __missing__(self, key):
value = open_picture(key)
self[key] = value
return value
pictures = Pictures()
handle = pictures[path]
handle.seek(0)
image_data = handle.read()
print(pictures)
print(image_data)