Python thread lifecycle

Question

I am threading noob here and would like your opinion on the life cycle on the following code:

import threading

def foo():
    .
    .
    .
    some_var = {}
    bar = threading.Thread(upload_S3(), kwargs = {...}) # Takes couple of seconds
    return some_var

Question: does return from foo() execute only after bar has finished or does return execute immediately even though the thread from bar has not finished executing.

TIA