机制:
try:
print('try...')
r = 10 / 0
print('result:', r)
except ZeroDivisionError as e:
print('except:', e)
finally:
print('finally...')
print('END')
多个except来捕获不同类型的错误:
try:
print('try...')
r = 10 / int('a')
print('result:', r)
except ValueError as e:
print('ValueError:', e)
except ZeroDivisionError as e:
print('ZeroDivisionError:', e)
finally:
print('finally...')
print('END')
当没有错误发生时,会自动执行else语句:
try:
print('try...')
r = 10 / int('2')
print('result:', r)
except ValueError as e:
print('ValueError:', e)
except ZeroDivisionError as e:
print('ZeroDivisionError:', e)
else:
print('no error!')
finally:
print('finally...')
print('END')
跨越多层调用:
def foo(s):
return 10 / int(s)
def bar(s):
return foo(s) * 2
def main():
try:
bar('0')
except Exception as e:
print('Error:', e)
finally:
print('finally...')
$ python3 err.py
Traceback (most recent call last):
File "err.py", line 11, in
main()
File "err.py", line 9, in main
bar('0')
File "err.py", line 6, in bar
return foo(s) * 2
File "err.py", line 3, in foo
return 10 / int(s)
ZeroDivisionError: division by zero
从上往下追踪错误信息
logging模块:
# err_logging.py
import logging
def foo(s):
return 10 / int(s)
def bar(s):
return foo(s) * 2
def main():
try:
bar('0')
except Exception as e:
logging.exception(e)
main()
print('END')
定义一个错误的class,用raise语句抛出:
# err_raise.py
class FooError(ValueError):
pass
def foo(s):
n = int(s)
if n==0:
raise FooError('invalid value: %s' % s)
return 10 / n
foo('0')
执行:
$ python3 err_raise.py
Traceback (most recent call last):
File "err_throw.py", line 11, in
foo('0')
File "err_throw.py", line 8, in foo
raise FooError('invalid value: %s' % s)
__main__.FooError: invalid value: 0
def foo(s):
n = int(s)
assert n != 0, 'n is zero!'
return 10 / n
def main():
foo('0')
关闭:
$ python -O err.py
Traceback (most recent call last):
...
ZeroDivisionError: division by zero
import logging
logging.basicConfig(level=logging.INFO)
s = '0'
n = int(s)
logging.info('n = %d' % n)
print(10 / n)
$ python err.py
INFO:root:n = 0
Traceback (most recent call last):
File "err.py", line 8, in
print(10 / n)
ZeroDivisionError: division by zero
python -m pdb err.py
输入命令l来查看代码:
(Pdb) l
1 # err.py
2 -> s = '0'
3 n = int(s)
4 print(10 / n)
输入命令p 变量名来查看变量:
(Pdb) p s
'0'
(Pdb) p n
0
输入命令q结束调试,退出程序:
(Pdb) q
# err.py
import pdb
s = '0'
n = int(s)
pdb.set_trace() # 运行到这里会自动暂停
print(10 / n)
用命令p查看变量,或者用命令c继续运行:
$ python err.py
> /Users/michael/Github/learn-python3/samples/debug/err.py(7)()
-> print(10 / n)
(Pdb) p n
0
(Pdb) c
Traceback (most recent call last):
File "err.py", line 7, in
print(10 / n)
ZeroDivisionError: division by zero
mydict.py定义 Dict 类:
class Dict(dict):
def __init__(self, **kw):
super().__init__(**kw)
def __getattr__(self, key):
try:
return self[key]
except KeyError:
raise AttributeError(r"'Dict' object has no attribute '%s'" % key)
def __setattr__(self, key, value):
self[key] = value
mydict_test.py测试:
import unittest
from mydict import Dict
class TestDict(unittest.TestCase):
def test_init(self):
d = Dict(a=1, b='test')
self.assertEqual(d.a, 1)
self.assertEqual(d.b, 'test')
self.assertTrue(isinstance(d, dict))
def test_key(self):
d = Dict()
d['key'] = 'value'
self.assertEqual(d.key, 'value')
def test_attr(self):
d = Dict()
d.key = 'value'
self.assertTrue('key' in d)
self.assertEqual(d['key'], 'value')
def test_keyerror(self):
d = Dict()
with self.assertRaises(KeyError):
value = d['empty']
def test_attrerror(self):
d = Dict()
with self.assertRaises(AttributeError):
value = d.empty
在mydict_test.py的最后加上两行代码:
if __name__ == '__main__':
unittest.main()
$ python mydict_test.py
或者
$ python -m unittest mydict_test
.....
----------------------------------------------------------------------
Ran 5 tests in 0.000s
OK
class TestDict(unittest.TestCase):
def setUp(self):
print('setUp...')
def tearDown(self):
print('tearDown...')
# mydict2.py
class Dict(dict):
'''
Simple dict but also support access as x.y style.
>>> d1 = Dict()
>>> d1['x'] = 100
>>> d1.x
100
>>> d1.y = 200
>>> d1['y']
200
>>> d2 = Dict(a=1, b=2, c='3')
>>> d2.c
'3'
>>> d2['empty']
Traceback (most recent call last):
...
KeyError: 'empty'
>>> d2.empty
Traceback (most recent call last):
...
AttributeError: 'Dict' object has no attribute 'empty'
'''
def __init__(self, **kw):
super(Dict, self).__init__(**kw)
def __getattr__(self, key):
try:
return self[key]
except KeyError:
raise AttributeError(r"'Dict' object has no attribute '%s'" % key)
def __setattr__(self, key, value):
self[key] = value
if __name__=='__main__':
import doctest
doctest.testmod()