On 2020-12-16 16:04, Rob Rosengard wrote:
Warning: I am new to this group
Warning: I am not an expert at Python, I've written a few small programs, and
spend 20 hours of online classes, and maybe a book or two.
Warning: I am new to trying to use concurrent.futures.ProcessPoolExecutor
- Prior to writing this question I updated to Python 3.9 and PyCharm 2020.3.
And confirmed the problem still exists.
- Running on Windows 10 Professional
- I've been trying to run a simple piece of code to exactly match what I have
seen done in various training videos. By I am getting a different and
unexpected set of results. I.e. the instructor got different results than I
did on my computer. My code is very simple:
import concurrent.futures
import time
start = time.perf_counter()
def task(myarg):
print(f'Sleeping one second...{myarg}')
time.sleep(1)
return 'Done sleeping...'
if __name__ == '__main__':
with concurrent.futures.ProcessPoolExecutor() as executor:
future1 = executor.submit(task, 1)
future2 = executor.submit(task, 2)
finish = time.perf_counter()
print(f'Finished in {round(finish-start,2)} seconds')
And the output is:
Finished in 0.0 seconds
Finished in 0.0 seconds
Sleeping one second...1
Sleeping one second...2
Finished in 1.14 seconds
Process finished with exit code 0
---
QUESTIONS and CONCERNS that I have...
It seems that both calls to task not only runs that function, but then keeps executing
the rest of the main line code. I only expected it to run the function and then
immediately quit/disappear. That is, I expect the output to look like (i.e. not having
the three lines of "Finished in x.x seconds", rather, just one line like that):
Sleeping one second...1
Sleeping one second...2
Finished in 1.14 seconds
Goal: I need the executor tasks to only run that one function, and then
completely go away and stop. Not keep executing more code that doesn't belong
to the task function.
I've tried many iterations of this issue, and placed PRINT statements all over
to try to track what is going on. And I used if/else statements in the main
code, which caused even more problems. I.e. both the IF and the ELSE was
executed each time through the code. Which completely blows my mind.
Any thoughts on this? Thanks for your time and help!
It imports the module to run the function, so any top-level code _will_
be run.
Here's a modified version:
--8<----------------------------8<--
import concurrent.futures
import time
print('Main code, __name__ is {!a}'.format(__name__))
start = time.perf_counter()
def task(myarg):
print('In task, __name__ is {!a}'.format(__name__))
print(f'Sleeping one second...{myarg}')
time.sleep(1)
return 'Done sleeping...'
if __name__ == '__main__':
with concurrent.futures.ProcessPoolExecutor() as executor:
future1 = executor.submit(task, 1)
future2 = executor.submit(task, 2)
finish = time.perf_counter()
print(f'Finished in {round(finish-start,2)} seconds')
--8<----------------------------8<--
It prints:
--8<----------------------------8<--
Main code, __name__ is '__main__'
Main code, __name__ is '__mp_main__'
Finished in 0.0 seconds
Main code, __name__ is '__mp_main__'
Finished in 0.0 seconds
In task, __name__ is '__mp_main__'
Sleeping one second...1
In task, __name__ is '__mp_main__'
Sleeping one second...2
Finished in 1.8 seconds
--8<----------------------------8<--
Any top-level code that you don't want it to run when it re-imports the
module should be protected by the __name__ test.
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