Python Decorators

Basic Decorator Implementation

import time
def main():
    time.sleep(3)
    print('Executing main function')
    
def secondary():
    print('Executing secondary function')
    
def utility():
    print('Executing utility function')
    
def timer_decorator(func_name):
    def wrapper():
        # Record start time
        start = time.time()
        func_name()
        # Record end time
        end = time.time()
        print(f'Total execution time: {end - start} seconds')
    return wrapper

main = timer_decorator(main)
main()

Handling Function Parameters

import time
def main():
    time.sleep(3)
    print('Executing main function')
    
def profile(user_id, **credentials):
    print('Executing profile function')
    return 'Profile data retrieved'

def utility():
    print('Executing utility function')
    
def timer_decorator(func_name):
    def wrapper(*args, **kwargs):
        # Record start time
        start = time.time()
        result = func_name(*args, **kwargs)
        # Record end time
        end = time.time()
        print(f'Total execution time: {end - start} seconds')
        return result
    return wrapper

main = timer_decorator(main)
main()

profile = timer_decorator(profile)
response = profile('user123', username='jerry', age=18)
print(response)

Standard Decorator Template

def main():
    pass

def decorator(func_name):
    def wrapper(*args, **kwargs):
        # Pre-function functionality
        result = func_name(*args, **kwargs)
        # Post-function functionality
        return result
    return wrapper

# Decorators本质上还是函数！

@decorator
def main():
    pass

# The decorator principle:
# The decorated object is passed as a parameter to the decorator

Multiple Decorators

import time

def timing_decorator(func):
    def wrapper(*args, **kwargs):
        start = time.time()
        res = func(*args, **kwargs)
        end = time.time()
        print(f'Execution time: {end - start} seconds')
        return res
    return wrapper

def authentication_decorator(func):
    def wrapper():
        username = input('Username: >>>').strip()
        password = input('Password: >>>').strip()
        if username == 'admin' and password == 'secret':
            print('Authentication successful')
            func()
        else:
            print('Invalid credentials')
    return wrapper

@authentication_decorator
timing_decorator
def main():
    time.sleep(3)
    print('Executing main function')

main()

Multiple Layer Decorators

# Predict the execution order of print statements
def outer1(func1):
    print('Loading outer1')
    def wrapper1(*args, **kwargs):
        print('Executing wrapper1')
        res1 = func1(*args, **kwargs)
        return res1
    return wrapper1

def outer2(func2):
    print('Loading outer2')
    def wrapper2(*args, **kwargs):
        print('Executing wrapper2')
        res2 = func2(*args, **kwargs)
        return res2
    return wrapper2

def outer3(func3):
    print('Loading outer3')
    def wrapper3(*args, **kwargs):
        print('Executing wrapper3')
        res3 = func3(*args, **kwargs)
        return res3
    return wrapper3

@outer1
@outer2
@outer3
def main():
    print('Executing main function')
    
main()

Decorator Preservation Techniques

import time
from functools import wraps

def decorator(func):
    @wraps(func)
    def wrapper():
        start = time.time()
        func()
        end = time.time()
        print(f'Execution time: {end - start} seconds')
    return wrapper

def main():
    '''This is the main function'''
    print('Executing main function')

@decorator
def secondary():
    '''This is the secondary function'''
    print('Executing secondary function')

help(secondary)

Parameterized Decorators

def authentication_handler(source_type, *args, **kwargs):
    def decorator(func):
        def wrapper(*args, **kwargs):
            username = input('Username: >>>').strip()
            password = input('Password: >>>').strip()
            
            # Retrieve credentials based on source type
            if source_type == 'file':
                print('Retrieving credentials from file')
            elif source_type == 'database':
                print('Retrieving credentials from database')
            elif source_type == 'api':
                print('Retrieving credentials from API')
            elif source_type == 'ldap':
                print('Retrieving credentials from LDAP')
            
            if username == 'admin' and password == 'secret':
                print('Authentication successful')
                func(source_type, *args, **kwargs)
            else:
                print('Invalid credentials')
        return wrapper
    return decorator

@authentication_handler('file', 1, 2, 3, 4, 5)
def profile():
    pass

profile('database')