Daemon Threads

What is a daemon thread?

A daemon thread is a background thread.

If only daemon threads are left running, Python can exit.
Non-daemon threads keep the program alive.

Example

daemon_thread.py

import threading
import time
 
 
def background():
    while True:
        print("background working...")
        time.sleep(0.5)
 
 
t = threading.Thread(target=background, daemon=True)
t.start()
 
time.sleep(2)
print("Main thread exiting")

daemon_thread.py

import threading
import time
 
 
def background():
    while True:
        print("background working...")
        time.sleep(0.5)
 
 
t = threading.Thread(target=background, daemon=True)
t.start()
 
time.sleep(2)
print("Main thread exiting")

When to use daemon threads

logging/reporting loops
background monitoring

When NOT to use them

Don’t use daemon threads for work that must finish (e.g., writing critical data).

🧪 Try It Yourself

Exercise 1 – Create a Daemon Thread

Exercise 2 – Non-Daemon vs Daemon

Exercise 3 – Main Thread is Not a Daemon

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