当我有返回值时，Python 不返回任何值

Question

I'm making a refresher on recursion and i've made a python file like this:

#!/usr/bin/python
import sys

if (len(sys.argv)!=3):
    raise ValueError('Please provide two dimensions.')
else:
    pass

def plotLand(a,b):
    if(a==b):
        print(a)
        return a
    if(a<b):
        c=b%a
        b = c if(c!=0) else a
    else:
        c = a%b
        a = c if (c!=0) else b
    plotLand(a,b)
result = plotLand(int(sys.argv[1]),int(sys.argv[2]))
print(result)

I added the print(a) just to check if my function was returning a value. I call this file in linux terminal in this way:

python algorithms.py 1680 64

And this is my output:

80
None

The print function inside my recursive function is printing the value, but I'm not getting the return value of the function. The original function didn't have the print function, as I mentioned before.

Answer 1

Recursive functions work exactly like non-recursive functions – if you don't write return and a value, you're returning None , and you only return anything when a == b .

You need

return plotLand(a,b)

I also think that you could shorten your code to

def plotLand(a,b):
    small, large = sorted((a,b))
    remainder = large % small
    return plotLand(remainder, small) if remainder else a 

Answer 2

You only return for one condition. You can consider adding a default at the end of the function