How does this recursive function work?

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def mult(a, b):
if b == 1:
return a
else:
return a + mult(a, b-1)

print(mult(2, 4))

What I have tried:

I have tried to understand how come this code does a multiplication without having a multiplication operator with no success.

Posted 15-Aug-18 0:28am

Member 13949923

Updated 15-Aug-18 0:53am

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Herman<T>.Instance 15-Aug-18 6:35am

why didn't you debug?

Member 13949923 15-Aug-18 7:00am

"I've tried putting bunch of prints but it still doesn't show me how it does multiplication without a multiplication operator." Edit: I just got it why.

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OriginalGriff · Accepted Answer · 2018-08-15T00:42:00

Recursion is simple to understand: see "recursion" and it'll all be clear!

Your function calls itself with different parameters, and return to itself with the value each time when it's calculated.
Look at what happens with your code when you pass specific values: a == 2, b == 3
1) 2, 3 : b is not 1, so you call the function again, with a == 2, b == 2
1.1) 2, 2 : b is not 1, so you call the function again, with a == 2, b == 1
1.1.1) 2, 1 : b is one, so you return a: 2
1.2) returns to 2, 2: and returns the 2 you got from 1.1.1, plus 2 : 4
2) returns to 2, 3: and returns the 4 you got from 1.2, plus 2 : 6

So the whole function returns 6.

It's a poor example of recursion - a loop is a lot easier and more efficient - but just follow it through with a debugger, and you'll see what I mean.