python 39 lines · 6 steps

A thread-safe debounce decorator in Python

A decorator that delays a function until calls stop arriving, using a lock and a restartable timer.

Explained by highlit

Advanced decorators debounce threading closures concurrency

1import threading
2from functools import wraps
3 
4 
5def debounce(wait):
6    def decorator(fn):
7        lock = threading.Lock()
8        state = {"timer": None}
9 
10        @wraps(fn)
11        def wrapper(*args, **kwargs):
12            def call():
13                with lock:
14                    state["timer"] = None
15                fn(*args, **kwargs)
16 
17            with lock:
18                if state["timer"] is not None:
19                    state["timer"].cancel()
20                state["timer"] = threading.Timer(wait, call)
21                state["timer"].daemon = True
22                state["timer"].start()
23 
24        def cancel():
25            with lock:
26                if state["timer"] is not None:
27                    state["timer"].cancel()
28                    state["timer"] = None
29 
30        wrapper.cancel = cancel
31        return wrapper
32 
33    return decorator
34 
35 
36@debounce(0.3)
37def on_search_input(query):
38    results = search_index.query(query)
39    render(results)

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Debouncing collapses a burst of rapid calls into one execution after the activity settles.
2A shared mutable dict plus a lock lets nested closures coordinate state safely across threads.
3Attaching a method to the returned wrapper extends a decorated function without changing its signature.

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