When Python evaluates odd( n ), first it evaluates n ; second, it assigns this argument value to the local parameter of odd (named spin); third, it applies odd, the suite of statements is executed, ending with return 1 or return 0; fourth, this result returned to the calling statement so that it can finish it's execution.

We would use this function like this.

s = random.randrange(37) 
# 0 <= s <= 36, single-0 roulette
if s == 0:
    print "zero"
elif odd(s):
    print s, "odd"
else:
    print s, "even"

We evaluate a function named random.randrange to create a random number, s. The if clause handles the case where s is zero. The first elif clause evaluates our odd function. To do this evaluation, Python must set spin to the value of s and execute the suite of statements that are the body of odd. The suite of statements will return either True or False. Since the if and elif clauses handle zero and odd cases, all that is left is for s to be even.