Simple Multithreading example in Python

threading_demo.py

#!/usr/bin/env python3
'''
Simple multithreading demo. Written 4/7/23 by Josh Jeppson (ifndefJOSH).

No warranty is given or implied. This was written to show a coworker how to get started with multithreading in Python.
'''
import threading
from os import cpu_count

# This will allow someTask() to take varied amounts of time
# to complete, much like real-world multithreading problems
import random
from time import sleep

# Number of threads to create
# This creates as many as there are logical CPU cores
N_THREADS = cpu_count()

# This is the number of times the information in someTask()
# will print to the screen
PRINT_ITERATIONS = 5

def someTask(n = 0):
	'''
This is the function we will be running on multiple CPUs. Or rather,
this function will be run multiple times, once per CPU
	'''
	# Print hello world from our threads
	for _ in range(PRINT_ITERATIONS):
		sleep(random.random() * 2) # Each thread can wait 0-2 s before printing
		print(f"Hello world from thread {n}")

if __name__=="__main__":
	threads = [threading.Thread(
		# Do not put the "()" at the end of the function name
		# You want the function pointer, NOT an invocation of the
		# function yet
		target = someTask
		# This is a tuple which allows you to specify the args to the function
		, args = (n, )
		) for n in range(N_THREADS)
	]
	# Starts each of the threads in the array of threads
	for thread in threads:
		thread.start()
	# Waits for each thread to finish. If you don't have this
	# then the program stops and the threads do not finish.
	# Also, this MUST be separate from the loop that starts them all
	for thread in threads:
		thread.join()

Example output (on a system with 8 logical cores):

Hello world from thread 2
Hello world from thread 0
Hello world from thread 1
Hello world from thread 5
Hello world from thread 6
Hello world from thread 4
Hello world from thread 0
Hello world from thread 3
Hello world from thread 3
Hello world from thread 7
Hello world from thread 2
Hello world from thread 3
Hello world from thread 3
Hello world from thread 6
Hello world from thread 0
Hello world from thread 1
Hello world from thread 5
Hello world from thread 7
Hello world from thread 4
Hello world from thread 5
Hello world from thread 3
Hello world from thread 5
Hello world from thread 2
Hello world from thread 6
Hello world from thread 0
Hello world from thread 4
Hello world from thread 2
Hello world from thread 7
Hello world from thread 1
Hello world from thread 1
Hello world from thread 5
Hello world from thread 6
Hello world from thread 7
Hello world from thread 1
Hello world from thread 6
Hello world from thread 0
Hello world from thread 4
Hello world from thread 7
Hello world from thread 2
Hello world from thread 4