how this code function?

Question

guys im doing the python course and i am at recursion. this code is a code of a exercise and the result is 5 but i don't know how this code function. can anyone say me how it works? thanks
0 Pl
def fib(x) :
if x == 0 or x == 1:
return 1
else:
return fib(x-1) + fib(x-2)

Answer 1

Simone

def fib(x) :
if x == 0 or x == 1:
return 1
else:
return fib(x - 1) + fib(x - 2)

print (fib(4))

#fib(3) + fib(2)
#fib(2) + fib(1) + fib(1) + fib(0)
#fib(1) + fib(0) + fib(1) + fib(1) + fib(0)
#1 + 1 + 1 + 1 + 1
#5

Answer 2

This is an example of recursive function. A recursive function is a function which calls itself repeatedly until a termination condition is met, after when it returns a value. Here your function works as below for the call fib(4):

fib(4)

fib(3) + fib(2)

fib(2)+fib(1) + fib(1)+fib(0)

fib(2)+ 1 + 1 + 1

fib(1)+fib(0) + 3

1 + 1 + 3

5

And finally return the value 5. Hope you understood =)

Answer 3

ok thank very much, now i understand