python - Program running forever if not inside the condition

Question

I have a question regarding this code:

import time
from concurrent.futures import ProcessPoolExecutor
 
# SINGLE PROCESS
 
 
def ask_user():
    start = time.time()
    user_input = input('Enter your name: ')
    greet = f'Hello, {user_input}'
    print(greet)
    print('ask_user: ', time.time() - start)
 
 
def complex_calculation():
    print('Started calculating...')
    start = time.time()
    [x**2 for x in range(10)]
    print('complex_calculation: ', time.time() - start)
 
 
# With a single thread, we can do one at a time—e.g.
start = time.time()
ask_user()
complex_calculation()
print('Single thread total time: ', time.time() - start, '

')
 
 
# TWO PROCESSES
 
 
# With two processes, we can do them both at once...
start = time.time()
if __name__ == '__main__':
    with ProcessPoolExecutor(max_workers=2) as pool:
        pool.submit(complex_calculation)
        pool.submit(complex_calculation)
 
    print('Two process total time: ', time.time() - start)

When I run it, it runs forever, but if I put all the code inside the condition block, then it works well:

import time
from concurrent.futures import ProcessPoolExecutor
 
# SINGLE PROCESS
 
 
def ask_user():
    start = time.time()
    user_input = input('Enter your name: ')
    greet = f'Hello, {user_input}'
    print(greet)
    print('ask_user: ', time.time() - start)
 
 
def complex_calculation():
    print('Started calculating...')
    start = time.time()
    [x**2 for x in range(10)]
    print('complex_calculation: ', time.time() - start)
 
 

if __name__ == '__main__':
    # With a single thread, we can do one at a time—e.g.
    start = time.time()
    ask_user()
    complex_calculation()
    print('Single thread total time: ', time.time() - start, '

')
 
 
    # TWO PROCESSES
 
 
    # With two processes, we can do them both at once...
    start = time.time()
    with ProcessPoolExecutor(max_workers=2) as pool:
        pool.submit(complex_calculation)
        pool.submit(complex_calculation)
 
    print('Two process total time: ', time.time() - start)

I guess that it has something to do with how Python calls modules and recursion but I don't have much idea other than that, so my question is - why does the first code run forever and second doesn't?

question from:https://stackoverflow.com/questions/65908870/program-running-forever-if-not-inside-the-condition

Answer 1

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