How do you use decorators in Python?
Decorators are tools in Python for extending function behavior. 1. The decorator is essentially a callable object that receives a function as a parameter and returns the wrapped function; 2. Use the @decorator_name syntax to apply the decorator, such as @logger or @repeat(3); 3. Common uses include logging, permission control, cache and routing binding (such as the Flask framework); 4. Notes include correctly returning the wrapper function, using functools.wraps to retain metadata, and the execution order of multiple decorators is nested from bottom to top.
Using decorators in Python can feel a bit confusing at first, but once you get the idea, they're a powerful way to modify or enhance functions without changing their actual code. At their core, decorators are just functions (or classes) that wrap another function to add functionality.
What Exactly Is a Decorator?
In simple terms, a decorator is a callable (like a function or class) that takes another function as an argument and extends its behavior without explicitly modifying it.
For example, imagine you want to log when certain functions are called. Instead of adding print statements inside each function, you can create a @logger decorator and put it above any function you want to track.
Here's a basic structure:
def my_decorator(func):
def wrapper():
print("Before function call")
func()
print("After function call")
Return wrapper
@my_decorator
def says_hello():
print("Hello")
say_hello()This will output:
Before function call Hello After function call
How to Create and Use Your Own Decorator
Creating your own decorator usually involves nesting functions. Here's how to do it step by step:
- Start with a function that takes another function (
func) as an argument. - Define a wrapper function inside it that does something before and/or after calling
func. - Return the wrapper function from the outer function.
- Apply the decorator using the
@decorator_namesyntax right above the target function.
If your decorated function needs to accept arguments, use *args and **kwargs in the wrapper so it can handle any number of positional and keyword arguments.
Example:
def repeat(num_times):
def decorator(func):
def wrapper(*args, **kwargs):
for _ in range(num_times):
result = func(*args, **kwargs)
return result
Return wrapper
Return decorator
@repeat(3)
def greet(name):
print(f"Hello {name}")
greet("Alice")This will print "Hello Alice" three times.
Common Uses for Decorators
You'll often see decorators used in these common scenarios:
- ? Adding logging, timing, or access control to functions
- ? Implementing authentication or permissions in web frameworks like Flask or Django
- ? Caching results (eg, using
@lru_cache) - ? Converting functions into properties (
@property) or static methods (@staticmethod)
These uses help keep your code clean and reusable. For instance, in Flask:
@app.route('/home')
def home():
return "Welcome!" The @app.route() decorator connects the URL /home to the home() function.
A Few Things to Watch Out For
Decorators are super useful, but there are some gotchas:
- ✅ Always remember to return the wrapper function inside your decorator — not call it.
- ❗ If you don't use
functools.wraps, the metadata (like.__name__) of the original function might be lost. - ⚠️ Order matters when stacking multiple decorators — they run from bottom to top.
So this:
@decorator1
@decorator2
def func():
passIs equivalent to:
decorator1(decorator2(func))
Also, if you're debugging, it can be surprised to see a decorated function reporting the name of the wrapper unless you use @functools.wraps .
Basically that's it. Once you understand the pattern — wrapping functions to extend behavior — you can start building your own or reading others' more easily.
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