🟡 Advanced Python · Lesson 21

Python Decorators

Python Decorators क्या है?

Python Decorators ka matlab hai: A decorator adds extra behavior to a function without changing the original function code. Simple words me, ye topic practical Python programs likhne me direct use hota hai.

Is topic ko sirf definition ke liye nahi, balki adding logging or timing jaise real examples ke liye practice karein.

यह क्यों सीखना जरूरी है?

Ye adding logging or timing me kaam aata hai.
Ye checking permissions se bhi connected hai.
Isse aap code ka output aur errors better samajh paate hain.

Important Terms

Term	Meaning
wrapper	Inner function used by a decorator to add extra behavior.
higher-order function	Function that accepts another function or returns a function.
@decorator	Syntax used to apply a decorator above a function.
logging	logging is an important term in this topic.
reuse	Using a saved model again without retraining.

Syntax / Basic Pattern

Basic idea: pehle data तैयार करें, phir Python logic apply करें, aur finally result display करें.

Basic Pattern

def simple_logger(func):
    def wrapper():
        print("Function started")
        func()
        print("Function ended")
    return wrapper
@simple_logger
def greet():

Complete Example Program

Python – decorators.py

def simple_logger(func):
    def wrapper():
        print("Function started")
        func()
        print("Function ended")
    return wrapper

@simple_logger
def greet():
    print("Hello Python")

greet()

Expected Output

Function started Hello Python Function ended

Program Explanation

def simple_logger(func): creates a reusable function.
def wrapper(): creates a reusable function.
print("Function started") displays information or calculated result on the screen.
func() performs the next step of the program logic.
print("Function ended") displays information or calculated result on the screen.
return wrapper sends a result back from the function.
@simple_logger performs the next step of the program logic.

Practical Uses

Adding logging or timing.
Checking permissions.
Reusing extra behaviour.

Common Mistakes

Making code complex when a simple function or class is enough.
Not handling possible errors or edge cases.
Mixing project dependencies instead of using a virtual environment.

Practice Tasks

Program ko decorators.py file me type karke run karein.
Values change karke output compare karein.
adding logging or timing par ek छोटा example banayen.
Logic ko apne words me 5 lines me likhein.

सारांश

Decorators in Python ko tab complete maanenge jab aap iska meaning, example, output aur practical use clearly explain kar saken.

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