Python-打印功能输出

Question

def cent_to_fahr(cent):
    print (cent / 5.0 * 9 + 32)

print (cent_to_fahr(20))

The output is this :

68.0
None

Why this output has None ?

I didn't get this result when I use just cent_to_fahr(20) . Can I ask why it happens ?

Answer 1

def cent_to_fahr(cent):
    return (cent / 5.0 * 9 + 32)

print (cent_to_fahr(20))

a function needs to return a value to have an output other then None

Answer 2

To put it into context, let's try understand what causes each line of output you received:

• 68.0 is printed thanks to the contents of your function. This could be seen as the "end" of that computation's "life", that value/result is no longer available for further computations.
• None is what the function returns , and in this case is also quite useless.
  
  

Now that we understand that better, I would recommend adjusting the function to return the value computed.

def cent_to_fahr(cent):
    return (cent / 5.0 * 9 + 32)

That way when the function is called (in context of further functions) it will return a value that that can be further processed (in this case with print() ):

>>>print(cent_to_fahr(20))

Which will print 68.0 .