python从函数差异返回的两种方法

Question

I would like to know if there are any relevant difference in functions below:

def function1(n):
    if n%2 == 0:
        return n
    else:
        return "Number " +str(n)+ " is odd."

and

def function2(n):
    if n%2 == 0:
        return n
    else:
        print "Number " +str(n)+ " is odd."
        return

In some online course I noticed that in one task (deffinitely more complex code than that printed above, but I made it simple to show just only a concept) automated grading was returning me an error that function did not exit normally when I used design from function1 and when I changed to design from function2 I got full score. I am really intrested why I could not use function1 as correct design, maybe somebody with more than I expierence will explain a bit and show correct with short explanation.

Answer 1

Your second function if the else is executed will return None where in the first it will return the value of "Number " +str(n)+ " is odd."

So if to need to use the value in the "Number " +str(n)+ " is odd." should the else be reached you would not be able to, you would only see it printed.

In [9]: x = function1(11)

In [10]: print x
Number 11 is odd.

In [11]: x = function2(11)
Number 11 is odd.

In [12]: print x
None

In your course the grader was more than likely not calling the functions using print so to see the output you would have to print function1(11) ,it is the same using any ide like pycharm etc.., just calling the function when you just have a return will not show the return value.

Without seeing the more complex code there are too many possibilities but one certain part of just printing is your function will return None which may well be required as a value elsewhere for code to terminate.