为什么在输出中打印“无"? [英] Why is this printing 'None' in the output?

问题描述

我定义了一个函数如下:

def 歌词():打印第一行"打印歌词()

但是为什么输出返回None:

第一行没有任何

解决方案

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.当函数不返回任何内容时，它隐式返回 None.

在函数末尾使用return语句返回值.

例如:

返回无.

<预><代码>>>>def test1():...打印功能中"....>>>a = test1()在功能上.>>>打印一个没有任何>>>>>>打印 test1()在功能上.没有任何>>>>>>测试1()在功能上.>>>

使用return语句

<预><代码>>>>定义测试():...返回ACV"...>>>打印测试()ACV>>>>>>a = 测试()>>>打印一个ACV>>>

I have defined a function as follows:

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

However why does the output return None:

The very first line
None

解决方案

Because there are two print statements. First is inside function and second is outside function. When a function doesn't return anything, it implicitly returns None.

Use return statement at end of function to return value.

e.g.:

Return None.

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

Use return statement

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

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