Is there a way to exit the other thread based on the value returned from another thread in python?

You can use Event Objects from threading.
You'll need to set an event object in your main method and use it as argument:

def main()
    # Initialise thread object
    flag = threading.Event()        
    start t1  # pass flag as arg
    start t2  # pass flag as arg
    t1.join
    t2.join

And your threading logic should be something like this

t1

if (condition is true):
    flag.set()

t2

while (not flag.is_set()):
    # Logic
    return

Here's another real, non-pseudo example

import threading


def main():
    # Initialise thread object
    flag = threading.Event()
    for i in range(2):
        if i == 0:
            t1 = threading.Thread(target=t1_func, args=(flag,))
            t1.start()
        else:
            t2 = threading.Thread(target=t2_func, args=(flag,))
            t2.start()


def t1_func(flag):
    for i in range(100000000):
        if i == 100000000 - 1:
            flag.set()


def t2_func(flag):
    while not flag.is_set():
        print('not flag yet')
    print('GOT FLAG !')


if __name__ == '__main__':
    main()

not flag yet
not flag yet
not flag yet
GOT FLAG !

Hope that's helpful and clear.