Decorators

Enhance functions and classes with Python decorators

What are Decorators?

Functions that modify other functions or classes
Use @ symbol to apply decorators
Allow adding functionality without modifying original code
Common for logging, timing, authentication, etc.

# Simple decorator
def my_decorator(func):
    def wrapper():
        print("Before function")
        func()
        print("After function")
    return wrapper

@my_decorator
def say_hello():
    print("Hello!")

say_hello()

Decorators with Arguments

Use *args and **kwargs to accept any arguments
Wrapper function passes arguments to original function
Preserves function signature
Can modify arguments before passing them

# Decorator with arguments
def repeat(times):
    def decorator(func):
        def wrapper(*args, **kwargs):
            for _ in range(times):
                result = func(*args, **kwargs)
            return result
        return wrapper
    return decorator

@repeat(3)
def greet(name):
    print(f"Hello {name}!")

greet("Alice")

Built-in Decorators

@staticmethod - method doesn't need instance or class
@classmethod - method receives class as first argument
@property - makes method accessible like an attribute
Common in object-oriented programming

class MyClass:
    class_var = "I am a class variable"
    
    def __init__(obj, value):
        obj._value = value
    
    @staticmethod
    def static_method():
        print("Static method called")
    
    @classmethod
    def class_method(cls):
        print(f"Class method: {cls.class_var}")
    
    @property
    def value(obj):
        return obj._value
    
    @value.setter
    def value(obj, new_value):
        obj._value = new_value

# Usage
obj = MyClass(10)
MyClass.static_method()
MyClass.class_method()
print(obj.value)
obj.value = 20

Practical Decorator Examples

Timing decorator to measure execution time
Logging decorator to track function calls
Caching decorator to store results
Authentication decorator for access control

import time

# Timing decorator
def timer(func):
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} took {end - start:.4f}s")
        return result
    return wrapper

@timer
def slow_function():
    time.sleep(1)
    print("Function completed")

slow_function()

# Logging decorator
def logger(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__}")
        result = func(*args, **kwargs)
        print(f"{func.__name__} returned {result}")
        return result
    return wrapper

@logger
def add(a, b):
    return a + b

add(5, 3)