c语言变量按其作用域分为_python的变量作用域详细

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#定义变量a

 代码如下 >>> a = 0
>>> print a

0#定义函数p()

 代码如下 >>> def p():
...  print a
...  
>>> p()

0#定义函数p2()

 代码如下 >>> 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

 代码如下 Traceback (most recent call last):
  File "", line 1, in
  File "", 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

 代码如下 ...  print a
...  
>>> p3()
3
>>> print a

0 # 外部变量a并未改变

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