PythonHow-ToBeginner · 4 min read

How to Use Threading Module in Python: Simple Guide

Use the threading module in Python by creating Thread objects with a target function and starting them with start(). Threads run tasks concurrently, allowing your program to do multiple things at once.

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Syntax

The basic syntax to use the threading module involves importing it, creating a Thread object with a target function, and starting the thread.

import threading: Loads the threading module.
threading.Thread(target=func): Creates a thread that will run the function func.
thread.start(): Starts the thread to run concurrently.
thread.join(): Waits for the thread to finish before continuing.

python

import threading

def worker():
    print('Worker thread is running')

thread = threading.Thread(target=worker)
thread.start()
thread.join()

Output

Worker thread is running

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Example

This example shows how to run two threads that print messages with a delay. It demonstrates how threads run at the same time, making the program faster for waiting tasks.

python

import threading
import time

def print_numbers():
    for i in range(1, 6):
        print(f'Number: {i}')
        time.sleep(1)

def print_letters():
    for letter in ['A', 'B', 'C', 'D', 'E']:
        print(f'Letter: {letter}')
        time.sleep(1)

thread1 = threading.Thread(target=print_numbers)
thread2 = threading.Thread(target=print_letters)

thread1.start()
thread2.start()

thread1.join()
thread2.join()

print('Both threads finished')

Output

Number: 1 Letter: A Number: 2 Letter: B Number: 3 Letter: C Number: 4 Letter: D Number: 5 Letter: E Both threads finished

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Common Pitfalls

Common mistakes when using threading include:

Not calling start() on the thread, so the function never runs.
Forgetting join(), which can cause the main program to exit before threads finish.
Accessing shared data without locks, causing data corruption.

Always use start() to run threads and join() to wait for them. Use threading.Lock() to protect shared data.

python

import threading

counter = 0
lock = threading.Lock()

def increment():
    global counter
    for _ in range(100000):
        with lock:
            counter += 1

threads = [threading.Thread(target=increment) for _ in range(2)]
for t in threads:
    t.start()
for t in threads:
    t.join()

print(f'Counter value: {counter}')

Output

Counter value: 200000

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Quick Reference

Method	Description
threading.Thread(target=func)	Create a new thread to run func
thread.start()	Start the thread's activity
thread.join()	Wait for the thread to finish
threading.Lock()	Create a lock to protect shared data
lock.acquire()/lock.release()	Manually lock and unlock (use with care)

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Key Takeaways

Create threads with threading.Thread and run them with start().

Use join() to wait for threads to finish before continuing.

Protect shared data with threading.Lock to avoid errors.

Threads run functions concurrently, speeding up waiting tasks.

Always start threads; just creating them does not run the code.