python 异常类型----后期需理解调整

1.Python内建异常体系结构
The class hierarchy for built-in exceptions is:

BaseException
 +-- SystemExit
 +-- KeyboardInterrupt
 +-- GeneratorExit
 +-- Exception
      +-- StopIteration
      +-- StandardError
      |    +-- BufferError
      |    +-- ArithmeticError
      |    |    +-- FloatingPointError
      |    |    +-- OverflowError
      |    |    +-- ZeroDivisionError
      |    +-- AssertionError
      |    +-- AttributeError
      |    +-- EnvironmentError
      |    |    +-- IOError
      |    |    +-- OSError
      |    |         +-- WindowsError (Windows)
      |    |         +-- VMSError (VMS)
      |    +-- EOFError
      |    +-- ImportError
      |    +-- LookupError
      |    |    +-- IndexError
      |    |    +-- KeyError
      |    +-- MemoryError
      |    +-- NameError
      |    |    +-- UnboundLocalError
      |    +-- ReferenceError
      |    +-- RuntimeError
      |    |    +-- NotImplementedError
      |    +-- SyntaxError
      |    |    +-- IndentationError
      |    |         +-- TabError
      |    +-- SystemError
      |    +-- TypeError
      |    +-- ValueError
      |         +-- UnicodeError
      |              +-- UnicodeDecodeError
      |              +-- UnicodeEncodeError
      |              +-- UnicodeTranslateError
      +-- Warning
           +-- DeprecationWarning
           +-- PendingDeprecationWarning
           +-- RuntimeWarning
           +-- SyntaxWarning
           +-- UserWarning
           +-- FutureWarning
       +-- ImportWarning
       +-- UnicodeWarning
       +-- BytesWarning
2.捕获异常的方式

方法一：捕获所有的异常

''' 捕获异常的第一种方式，捕获所有的异常 '''
    try:
        a = b
        b = c
    except Exception,data:
        print Exception,":",data
    '''输出：<type 'exceptions.Exception'> : local variable 'b' referenced before assignment ''
--------------------------------------------------------------------------------

方法二：采用traceback模块查看异常，需要导入traceback模块

''' 捕获异常的第二种方式，使用traceback查看异常 '''
    try:
        a = b
        b = c
    except:
        print traceback.print_exc()
    '''输出： Traceback (most recent call last):
          File "test.py", line 20, in main
                a = b
        UnboundLocalError: local variable 'b' referenced before assignmen
--------------------------------------------------------------------------------

方法三：采用sys模块回溯最后的异常

''' 捕获异常的第三种方式，使用sys模块捕获异常 '''
    try:
        a = b
        b = c
    except:
        info = sys.exc_info()
        print info
        print info[0]
        print info[1]
    '''输出：
    (<type 'exceptions.UnboundLocalError'>, UnboundLocalError("local variable 'b' referenced before assignment",),
    <traceback object at 0x00D243F0>)
    <type 'exceptions.UnboundLocalError'>
    local variable 'b' referenced before assignment
    '''
-------------------------------------------------------------------------------

1、NameError：尝试访问一个未申明的变量
>>>  v
NameError: name 'v' is not defined

2、ZeroDivisionError：除数为0
>>> v = 1/0
ZeroDivisionError: int division or modulo by zero

3、SyntaxError：语法错误
>>> int int
SyntaxError: invalid syntax (<pyshell#14>, line 1)

4、IndexError：索引超出范围
>>> List = [2]
>>> List[3]
Traceback (most recent call last):
  File "<pyshell#18>", line 1, in <module>
    List[3]
IndexError: list index out of range

5、KeyError：字典关键字不存在
>>> Dic = {'1':'yes', '2':'no'}
>>> Dic['3']
Traceback (most recent call last):
  File "<pyshell#20>", line 1, in <module>
    Dic['3']
KeyError: '3'

6、IOError：输入输出错误
>>> f = open('abc')
IOError: [Errno 2] No such file or directory: 'abc'

7、AttributeError：访问未知对象属性
>>> class Worker:
 def Work():
  print("I am working")

>>> w = Worker()
>>> w.a
Traceback (most recent call last):
  File "<pyshell#51>", line 1, in <module>
    w.a
AttributeError: 'Worker' object has no attribute 'a'

8、ValueError：数值错误
>>> int('d')
Traceback (most recent call last):
  File "<pyshell#54>", line 1, in <module>
    int('d')
ValueError: invalid literal for int() with base 10: 'd'

9、TypeError：类型错误
>>> iStr = '22'
>>> iVal = 22
>>> obj = iStr + iVal;
Traceback (most recent call last):
  File "<pyshell#68>", line 1, in <module>
    obj = iStr + iVal;
TypeError: Can't convert 'int' object to str implicitly

10、AssertionError：断言错误
>>> assert 1 != 1
Traceback (most recent call last):
  File "<pyshell#70>", line 1, in <module>
    assert 1 != 1
AssertionError

11、MemoryError:内存耗尽异常

12、NotImplementedError：方法没实现引起的异常

示例：

1 class Base(object):
2     def __init__(self):
3         pass
4
5     def action(self):
6         raise NotImplementedError

定义一个类，一个接口方法action,如果直接调用action则抛NotImplementedError异常，这样做的目的通常是用来模拟接口

13、LookupError：键、值不存在引发的异常

LookupError异常是IndexError、KeyError的基类

如果你不确定数据类型是字典还是列表时，可以用LookupError捕获此异常

14、StandardError 标准异常。

除StopIteration, GeneratorExit, KeyboardInterrupt 和SystemExit外，其他异常都是StandarError的子类。

异常处理有别于错误检测：

错误检测与异常处理区别在于：错误检测是在正常的程序流中，处理不可预见问题的代码，例如一个调用操作未能成功结束