Python ยท Chapter 31 of 45
Python Decorators
A DECORATOR is a function that wraps another function, adding behaviour before or after it. Use with `@decorator` syntax.
Common uses: logging, timing, caching, access control, and Flask/Django route registration.
How they work
A decorator takes a function and returns a new function. `@deco` above `def f():` is short for `f = deco(f)`.
functools.wraps
Use `@functools.wraps(func)` inside your decorator so the wrapped function keeps its original name and docstring.
Example 1 (python)
def log(func):
def wrapper(*args, **kw):
print(f"calling {func.__name__}")
return func(*args, **kw)
return wrapper
@log
def add(a, b):
return a + b
print(add(2, 3))Output
calling add
5Wraps add() with a logging step.
Example 2 (python)
from functools import lru_cache
@lru_cache
def fib(n):
return n if n < 2 else fib(n-1) + fib(n-2)
print(fib(30))Output
832040lru_cache caches results โ massive speedup for recursive functions.
Key points
- Function that wraps another function.
- Syntax: `@decorator` above `def`.
- Use `functools.wraps` to preserve metadata.
- Common built-ins: `@staticmethod`, `@classmethod`, `@property`, `@lru_cache`.
๐ก Note: Decorators run at function-definition time, not each call โ but the wrapper they return runs every call.