Python recursive function - can anyone explain me this code in detail

Question

def is_even(x):
if x == 0:
return True
else:
return is_odd(x-1)

def is_odd(x):
return not is_even(x)

print(is_odd(17))
print(is_even(23))

Answer 1

this is the biggest eyesore of a function i've ever seen.

to explain it in detail let's take a smaller number like 5:

is_even(5):

is 5 equal to 0? no
so, is_odd(4) gets called

is_odd(4) returns !(is_even(4))

is_even(4):

is 4 equal to 0? no
so, is_odd(3) gets called

is_odd(3) returns !(is_even(3))

is_even(3):

is 3 equal to 0? no
so, is_odd(2) gets called

is_odd(2) returns !(is_even(2))

is_even(2):

is 2 equal to 0? no
so, is_odd(1) gets called

is_odd(1) returns !(is_even(1))

is_even(1):

is 1 equal to 0? no
so, is_odd(0) gets called

is_odd(0) returns !(is_even(0))

is_even(0):

is 0 equal to 0? yes

is_even(0) returns true
is_odd(0) returns false (negation of is_even(0))
is_even(1) then returns the result of is_odd(0) (which is false)
is_odd(1) returns true
is_even(2) returns true (same like is_even 1)
is_odd(2) returns false
is_even(3) returns false
is_odd(3) returns true
is_even(4) returns true
is_odd(4) returns false

and finally

is_even(5) returns false, therefore concluding 5 is not even

Answer 2

Gagan Lohar well there's a condition that if it's 0 it returns true, and thus the odd one is a negation of it, returning false

Answer 3

Thank you for replying.....i really appreciate for your detailed answer....
but still i didn’t get the point that how even values returning true from 1st function and odd values returning false from 1st function

Answer 4

thank you so much hinanawi