python学习7 - 异常

定义异常

　　python 用异常对象（exception object）来表示异常情况，遇到错误后，会引发异常，如果异常对象未被捕捉或处理，程序就会用所谓的回溯　　　　（Tracebace）执行终止:

>>> 1/0

Traceback (most recent call last):
  File "<pyshell#99>", line 1, in <module>
    1/0
ZeroDivisionError: integer division or modulo by zero

 

　　raise: 自己引发异常，程序会自动创建实例

>>> raise Exception

Traceback (most recent call last):
  File "<pyshell#100>", line 1, in <module>
    raise Exception
Exception
>>> raise Exception("hahahahahaha")

Traceback (most recent call last):
  File "<pyshell#101>", line 1, in <module>
    raise Exception("hahahahahaha")
Exception: hahahahahaha

　　python 内建的异常类有很多，这些异常类都在exceptions 模块中

>>> dir(exceptions)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'EnvironmentError', 'Exception', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '__doc__', '__name__', '__package__']

　　一些重要的异常类

　　自定义异常类，只要这个异常类 继承 Exception

>>> calss AutoError(Exception):pass

 

捕捉异常

　　格式如下：

 

try:
    x = input("the first Num: ")
    y = input("the second Num: ")
    print x/y
except ZeroDivisionError:
    print "the second number cat't be zero"

the first Num: 10
the second Num: 0
the second number cat't be zero

 

ps:如果没有捕捉异常，它就会被调用他的函数的方法体内的 try 捕捉到，依次类推，也就是说 ，你可以捕捉到在其他人的函数中所引发的异常

　　多个except：

try:
    x = input("the first Num: ")
    y = input("the second Num: ")
    print x/y
except ZeroDivisionError:
    print "the second number cat't be zero"
except TypeError:
    print "That wasn't a number ,was it"

　　用一个块捕捉多个异常

try:
    x = input("the first Num: ")
    y = input("the second Num: ")
    print x/y
except (ZeroDivisionError,TypeError):
    print "the numbers was bug"

　　捕捉对象

try:
    x = input("the first Num: ")
    y = input("the second Num: ")
    print x/y
except (ZeroDivisionError,TypeError),e:    # 在python 3.0 中，格式为except (ZeroDivisionError,TypeError) as e

print e

　　全捕捉 --任何异常都不放过，呵呵

try:
    x = input("the first Num: ")
    y = input("the second Num: ")
    print x/y
except :
    print "hahaha"

 　　else --  在没有捕捉到异常情况下 出发

try:
    x = input("the first Num: ")
    y = input("the second Num: ")
    print x/y
except :
    print "hahaha"
else:
    print "it's ok"

　　Finally  -- 在可能的异常后进行清理，与 try  联合使用

try:
    1/0
except:
    print "err"
else:
    print "it's ok"
finally:
    print "Cleaning up"

>>> 
err
Cleaning up