forked from bslatkin/effectivepython
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathitem_080.py
More file actions
executable file
·198 lines (155 loc) · 4.77 KB
/
item_080.py
File metadata and controls
executable file
·198 lines (155 loc) · 4.77 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
192
193
194
195
196
197
198
#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2024 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.
### Start book environment setup
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)
### End book environment setup
print("Example 1")
def try_finally_example(filename):
print("* Opening file")
handle = open(filename, encoding="utf-8") # May raise OSError
try:
print("* Reading data")
return handle.read() # May raise UnicodeDecodeError
finally:
print("* Calling close()")
handle.close() # Always runs after try block
print("Example 2")
try:
filename = "random_data.txt"
with open(filename, "wb") as f:
f.write(b"\xf1\xf2\xf3\xf4\xf5") # Invalid utf-8
data = try_finally_example(filename)
# This should not be reached.
import sys
sys.exit(1)
except:
logging.exception('Expected')
else:
assert False
print("Example 3")
try:
try_finally_example("does_not_exist.txt")
except:
logging.exception('Expected')
else:
assert False
print("Example 4")
import json
def load_json_key(data, key):
try:
print("* Loading JSON data")
result_dict = json.loads(data) # May raise ValueError
except ValueError:
print("* Handling ValueError")
raise KeyError(key)
else:
print("* Looking up key")
return result_dict[key] # May raise KeyError
print("Example 5")
assert load_json_key('{"foo": "bar"}', "foo") == "bar"
print("Example 6")
try:
load_json_key('{"foo": bad payload', "foo")
except:
logging.exception('Expected')
else:
assert False
print("Example 7")
try:
load_json_key('{"foo": "bar"}', "does not exist")
except:
logging.exception('Expected')
else:
assert False
print("Example 8")
UNDEFINED = object()
DIE_IN_ELSE_BLOCK = False
def divide_json(path):
print("* Opening file")
handle = open(path, "r+") # May raise OSError
try:
print("* Reading data")
data = handle.read() # May raise UnicodeDecodeError
print("* Loading JSON data")
op = json.loads(data) # May raise ValueError
print("* Performing calculation")
value = op["numerator"] / op["denominator"] # May raise ZeroDivisionError
except ZeroDivisionError:
print("* Handling ZeroDivisionError")
return UNDEFINED
else:
print("* Writing calculation")
op["result"] = value
result = json.dumps(op)
handle.seek(0) # May raise OSError
if DIE_IN_ELSE_BLOCK:
import errno
import os
raise OSError(errno.ENOSPC, os.strerror(errno.ENOSPC))
handle.write(result) # May raise OSError
return value
finally:
print("* Calling close()")
handle.close() # Always runs
print("Example 9")
temp_path = "random_data.json"
with open(temp_path, "w") as f:
f.write('{"numerator": 1, "denominator": 10}')
assert divide_json(temp_path) == 0.1
print("Example 10")
with open(temp_path, "w") as f:
f.write('{"numerator": 1, "denominator": 0}')
assert divide_json(temp_path) is UNDEFINED
print("Example 11")
try:
with open(temp_path, "w") as f:
f.write('{"numerator": 1 bad data')
divide_json(temp_path)
except:
logging.exception('Expected')
else:
assert False
print("Example 12")
try:
with open(temp_path, "w") as f:
f.write('{"numerator": 1, "denominator": 10}')
DIE_IN_ELSE_BLOCK = True
divide_json(temp_path)
except:
logging.exception('Expected')
else:
assert False