Please help why are x and y being added together ? What am I missing

Question

def rec(x,y):
if x == 0:
return y:
if y != 0:
return rec( x-1, y+1)
print(rec(3,4))
# Output is 7
# why is it not (2,5)

Answer 1

It is a recursive function (it calls itself).
It has two arguments. If the first argument x is zero, the result is the other argument.
Otherwise x is decreased and y is increased, and the function is called with these new numbers again.

What happens effectively:
rec(3, 4) =
rec(2, 5) =
rec(1, 6) =
rec(0, 7) =
7 is returned through the call stack

Answer 2

Recursion is a tricky topic, I see you are doing the Python Beginner course and this is covered in the intermediate course.

Return is giving back a value to the place where the function was called. But in this case, the last line of the function returns a new invocation of the same function, which is yet to be calculated with the new values. This could go on forever, but in recursion we always have a "base case" which is supposed to stop this endless loop. In this one, the recursion is stopped when either X or Y reach 0.

Answer 3

O ok thanks I thought it was adding the two numbers 2 and 5. Also I thought you needed while or for to loop. Does the return start the sequence again. Your help is much appreciated I am very new to all this.

Answer 4

Thank you for your help. I understand it now. Its quite simple once I read it again. 👍

Answer 5

Because you return the def rec ,it will start the code again and again. It will go on forever until x or y is == 0.the function calls itself.. maybe someone more advanced could explain it better.

Answer 6

I can't understand that can you explain it !!!!

Answer 7

Each time X will -1 and y will + 1. It will stop once either == 0

Answer 8

def rec(x,y):
if x == 0:
return y # remove ":" (The colon)
if y != 0:
return ( x-1, y+1) # remove "rec"

print(rec(3,4))

Answer 9

Sorry the : after return was a misprint. It still adds X and y together. I am just not sure why

Answer 10

Why does putting the rec after the return add X and y

Answer 11

Ello