假如你的程序中有一些无效的语句，会怎么样呢？Python会引发并告诉你那里有一个错误，从而处理这样的情况。 常见Python错误 AttributeError 视图访问一个对象没有的属性，比如foo.x，但是foo没有属性x >>> a = (1,2,3) >>> a.append(4) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'tuple' object has no attribute 'append'IOError 输入/输出异常；基本上是无法打开文件
>>> f = open('linuxeye.txt')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'linuxeye.txt'
ImportError 无法引入模块和包；基本上市路径问题或者名称错误IndentationError 语法错误（的子类）；代码没有正确对齐 indexError 下标索引超出序列边界，比如当x只有三个元素，却试图访问x[5] >>> a = [1,2,3] >>> a[3] Traceback (most recent call last): File "<stdin>", line 1, in <module> IndexError: list index out of rangeKeyError 视图访问字典里不存在的键
>>> dict = {1:'first',2:'second',3:'three'}
>>> dict[4]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 4
KeyboardInterrupt Ctrl+C被按下NameError 使用一个还未被赋予对象的变量 SyntaxError Python代码非法，代码不能编译（语法错误） TypeError 传入对象类型与要求不相符 UnboundLocalError 视图访问一个还未被设置的局部变量，基本上是由于另有一个同样的全局变量导致你以为正在访问它 ValueError 传入一个调用者不期望的值，即使值得类型是正确的 try..except 把通常的语句放在try块中，而把我们的错误处理语句放在except块中
#!/usr/bin/env python
# Filename: try_except.py
import sys
try:
s = raw_input('Enter something --> ')
except EOFError:
print '\nWhy did you do an EOF on me?'
sys.exit() # exit the program
except:
print '\nSome error/exception occurred.'
# here, we are not exiting the program
print 'Done'
$ python try_except.py Enter something --> Why did you do an EOF on me? $ python try_except.py Enter something --> Learning Python Done 引发异常 使用raise语句引发异常。你还得指明错误/异常的名称和伴随异常触发的异常对象。你可以引发的错误或异常应该分别是一个Error或Exception类的直接或间接导出类
#!/usr/bin/env python
# Filename: raising.py
class ShortInputException(Exception):
'''A user-defined exception class.'''
def __init__(self, length, atleast):
Exception.__init__(self)
self.length = length
self.atleast = atleast
try:
s = raw_input('Enter something --> ')
if len(s) < 3:
raise ShortInputException(len(s), 3)
# Other work can continue as usual here
except EOFError:
print '\nWhy did you do an EOF on me?'
except ShortInputException, x:
print 'ShortInputException: The input was of length %d, \
was expecting at least %d' % (x.length, x.atleast)
else:
print 'No exception was raised.'
$ python raising.py Enter something --> Why did you do an EOF on me? $ python raising.py Enter something --> py ShortInputException: The input was of length 2, was expecting at least 3 $ python raising.py Enter something --> python No exception was raised. try ... finally 假如你在读一个文件的时候，希望在无论异常发生与否的情况下都关闭文件，该怎么做呢？这可以使用finally块来完成。注意，在一个try块下，你可以同时使用except从句和finally块。如果你要同时使用它们的话，需要把一个嵌入另外一个 |