Print statement inside function used within lambda function not executing

Question

In the code below, gen_window has a print statement in it but when I run the code the print statement doesn't get executed. Why is that and then how should I go about debugging such lambda functions? (Even the debugger ignores the breakpoint in these functions.)

getpairs = rdd.flatMap(lambda xi: gen_window(xi, n))


def gen_window(xi, n):
    x, i = xi
    l = []
    for offset in range(n):
        print("-->", (i - offset, (i, x)))
        l.append((i - offset, (i, x)))
    return l

Answer 1

Works:

def gen_window(xi, n):
    x, i = xi
    l = []
    for offset in range(n):
        print("-->", (i - offset, (i, x)))
        l.append((i - offset, (i, x)))
    return l

xi = [3,5]
n = 3

gen_window(xi, n)

Lambdas only get executed wenn you actually use them - If you get no output you are probably never using it.

Output:

--> (5, (5, 3))
--> (4, (5, 3))
--> (3, (5, 3))