为什么在输出中打印"无"？

Question

我已经定义了一个函数如下:

def lyrics():
    print "The very first line"
print lyrics()

但是为什么输出会返回None:

The very first line
None

Answer 1

因为有两个打印语句.第一个是内部功能,第二个是外部功能.当函数没有返回任何时候它返回无值.

return在函数末尾使用语句返回值.

例如:

返回无值.

>>> def test1():
...    print "In function."
... 
>>> a = test1()
In function.
>>> print a
None
>>> 
>>> print test1()
In function.
None
>>>
>>> test1()
In function.
>>> 

使用return语句

>>> def test():
...   return "ACV"
... 
>>> print test()
ACV
>>> 
>>> a = test()
>>> print a
ACV
>>> 

Answer 2

由于双重打印功能.我建议你使用return而不是print在函数定义中.

def lyrics():
    return "The very first line"
print lyrics()

要么

def lyrics():
    print "The very first line"
lyrics()