Python 为什么在输出中打印“无”？
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Why is this printing 'None' in the output?
提问by def_0101
I have defined a function as follows:
我定义了一个函数如下：
def lyrics():
print "The very first line"
print lyrics()
However why does the output return None:
但是为什么输出返回None：
The very first line
None
采纳答案by Vivek Sable
Because there are two print statements. First is inside function and second is outside function. When function not return any thing that time it return None value.
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。当函数不返回任何东西时，它返回 None 值。
Use returnstatement at end of function to return value.
return在函数末尾使用语句返回值。
e.g.:
例如：
Return None value.
返回无值。
>>> def test1():
... print "In function."
...
>>> a = test1()
In function.
>>> print a
None
>>>
>>> print test1()
In function.
None
>>>
>>> test1()
In function.
>>>
Use return statement
使用返回语句
>>> def test():
... return "ACV"
...
>>> print test()
ACV
>>>
>>> a = test()
>>> print a
ACV
>>>
回答by Avinash Raj
Because of double print function. I suggest you to use returninstead of printinside the function definition.
由于双打印功能。我建议你使用return而不是print在函数定义里面。
def lyrics():
return "The very first line"
print(lyrics())
OR
或者
def lyrics():
print("The very first line")
lyrics()
