Decorators & Context Managers

1️⃣ Function Decorators

Python me decorator ek function hota hai jo kisi dusre function ke behavior ko modify karta hai bina uske code ko directly change kiye. Ye @ symbol ke saath use hota hai.


def greet_decorator(func):
    def wrapper():
        print("👋 Hello!")
        func()
        print("🎉 Goodbye!")
    return wrapper

@greet_decorator
def say_name():
    print("Mera naam AIkiPadhai hai!")

say_name()

👉 Output:


👋 Hello!
Mera naam AIkiPadhai hai!
🎉 Goodbye!

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2️⃣ Decorator with Arguments

Kabhi kabhi function me arguments hote hain — decorator ko unhe handle karna hota hai using *args aur **kwargs.


def log_decorator(func):
    def wrapper(*args, **kwargs):
        print(f"Function '{func.__name__}' called with {args} {kwargs}")
        result = func(*args, **kwargs)
        print(f"Result: {result}")
        return result
    return wrapper

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

add(5, 10)

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3️⃣ Chaining Multiple Decorators

Multiple decorators ek function par lagaye ja sakte hain. Ye upar se neeche tak apply hote hain (top-down order me).


def star(func):
    def wrapper():
        print("⭐" * 10)
        func()
        print("⭐" * 10)
    return wrapper

def smile(func):
    def wrapper():
        print("😊")
        func()
        print("😊")
    return wrapper

@star
@smile
def greet():
    print("Namaste!")

greet()

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4️⃣ Class Decorators

Class decorators tab use karte hain jab aap kisi class ke behavior ko modify karna chahte ho.


def add_method(cls):
    cls.greet = lambda self: print("Hello from", self.__class__.__name__)
    return cls

@add_method
class Student:
    pass

s = Student()
s.greet()

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5️⃣ Context Managers (with Statement)

Context managers resource management ke liye hote hain — jaise file handle, network connection, ya database. with statement ensure karta hai ki resource safely open aur close ho.


with open("data.txt", "w") as f:
    f.write("AIkiPadhai Rocks!")
# file automatically closed yahan

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6️⃣ Custom Context Manager

Apna khud ka context manager banana easy hai using __enter__() aur __exit__().


class FileManager:
    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode

    def __enter__(self):
        print("Opening file...")
        self.file = open(self.filename, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_value, traceback):
        print("Closing file...")
        self.file.close()

with FileManager("sample.txt", "w") as f:
    f.write("Hello from context manager!")

---

7️⃣ contextlib Module

contextlib decorator ke saath ek function ko context manager bana sakte hain — short aur clean syntax me.


from contextlib import contextmanager

@contextmanager
def simple_manager():
    print("Enter...")
    yield
    print("Exit...")

with simple_manager():
    print("Working inside block...")