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Events (signal between threads)

What is an Event?

An EventEvent is a simple flag:

one thread sets it
other threads wait until it’s set

Example

event_example.py

import threading
import time
 
ready = threading.Event()
 
 
def waiter():
    print("Waiting...")
    ready.wait()  # blocks
    print("Go!")
 
 
def setter():
    time.sleep(1)
    ready.set()
 
 
t1 = threading.Thread(target=waiter)
t2 = threading.Thread(target=setter)
 
t1.start(); t2.start()
t1.join(); t2.join()

event_example.py

import threading
import time
 
ready = threading.Event()
 
 
def waiter():
    print("Waiting...")
    ready.wait()  # blocks
    print("Go!")
 
 
def setter():
    time.sleep(1)
    ready.set()
 
 
t1 = threading.Thread(target=waiter)
t2 = threading.Thread(target=setter)
 
t1.start(); t2.start()
t1.join(); t2.join()

Resetting an event

event.clear()event.clear() resets it to false.
Useful for repeated cycles.

🧪 Try It Yourself

Exercise 1 – threading.Event Set and Wait

Exercise 2 – Clear an Event

Exercise 3 – Event with Timeout

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