关于python的变量作用域

 

#定义变量a

>>> a = 0

>>> print a

0

#定义函数p()

>>> def p():

...     print a

...     

>>> p()

0

#定义函数p2()

>>> def p2():

...     print a

...     a = 3

...     print a

...     

>>> p2() # 运行出错，外部变量a先被引用，不能重新赋值

Traceback (most recent call last):

  File "input>", line 1, in <module>

  File "input>", line 2, in p2

UnboundLocalError: local variable 'a' referenced before assignment

#定义函数p3()

>>> def p3():

...     a = 3 # 不引用直接赋值

...     print a

...     

>>> p3()

3

>>> print a

0 # 外部变量a并未改变