错误处理：

两个版本的错误处理都有一个小的变化。在python 3.x中，'as'关键字是必需的。

try:

trying_to_check_error

except NameError, err:

print err, 'Error Caused' # Would not work in Python 3.x

'''

Output in Python 2.x:

name 'trying_to_check_error' is not defined Error Caused

Output in Python 3.x :

File "a.py", line 3

except NameError, err:

^

SyntaxError: invalid syntax

'''

在python2中：

try:

trying_to_check_error

except NameError as err: # 'as' is needed in Python 3.x

print (err, 'Error Caused')

'''

Output in Python 2.x:

(NameError("name 'trying_to_check_error' is not defined",), 'Error Caused')

Output in Python 3.x :

name 'trying_to_check_error' is not defined Error Caused

'''