Python 异常 (8) 持续更新

异常 当程序遇到时，会引发异常。

>>> 1 / 0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero

抛出一个自定义错误

>>> raise Exception("Custom Exception")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Exception: Custom Exception

dir 函数列出模块的内容

>>> import exceptions
>>> dir(exceptions)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'Buffer
Error', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'EnvironmentError', 'E
xception', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'I
mportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'Key
boardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'NotImplementedError
', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'R
untimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError',
 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TypeError', 'Unbound
LocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'Unicod
eTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'Win
dowsError', 'ZeroDivisionError', '__doc__', '__name__', '__package__']

自定义异常

# coding=utf-8

# 确定使用新式类
__metaclass__ = type


class MyException(Exception):
    def __init__(self, value):
        self.value = value

try:
    raise MyException(12)
except MyException as e:
    print 'Exception value:', e.value

输出

Exception value: 12

捕捉异常 try/except

# coding=utf-8

# 确定使用新式类
__metaclass__ = type

try:
    x = input('x:')
    y = input('y:')
    print x/y
except TypeError:
    print 'TypeError'
except ZeroDivisionError:
    print 'ZeroDivisionError'

try:
    x = input('x:')
    y = input('y:')
    print x/y
except (TypeError, ZeroDivisionError), e:
    print 'Error', e

except (TypeError, ZeroDivisionError), e:

except (TypeError, ZeroDivisionError) as e:

上面两句是一样的。

当没有任何错误时，可以用 try/except/else,看例子

while True:
    try:
        x = input('x:')
        y = input('y:')
        print x / y
    except Exception as e:
        print 'Error', e
    else:
        break

finally子句对可能的异常清理

while True:
    try:
        x = input('x:')
        y = input('y:')
        print x / y
    except Exception as e:
        print 'Error', e
    else:
        break
    finally:
        del x
        del y