Thread lets different parts of program run concurrently. Usually when you have a part of execution in your program that takes longer than usual to run, it’s better let it run in a thread without blocking the main program to handle the user’s interactions or other executions etc.

Thread in Python does not mean multi-processing, it still runs on a single processor. Functions run in different threads are simply taking turns to run.

import threading
import time
def my_func1():
   counter = 0 
   while counter < 100 :
      counter += 1
      print("counter is :"+str(counter))
      time.sleep(1)
   print("bye bye now")

def my_func2():
	txt = input() 
	while txt != 'x' :
		print("You've entered :" + txt +"\n")
		txt = input()
	print("bye, you've entered x")

In the above code, we have two functions my_func1 and my_func2.

Function my_func1 takes long time to execute, as it only exits when it's increased the counter to 100 and each time it'll take a one-second sleep; meaning you'll have to wait up to about 100 seconds then the following lines of instructions to be executed.

The function my_func2 keeps looping for the user's input at the command line and exits only when an "x" is entered.

thread1 = threading.Thread(target=my_func1)
thread1.start()

thread2 = threading.Thread(target=my_func2)
thread2.start()

In the above example we run the two functions in two separate threads, thus my_func1 and my_func2 will run concurrently, the output is as follows:

If my_func1 and my_func2 are not run in threads, then the program has to wait for my_func1 to finish first then only to run my_func2.