装饰器 decorator

装饰器

def document_it(func):
    def new_function(*args, **kwargs):
        print('Running function:', func.__name__)
        print('Positional arguments:', args)
        print('Keyword arguments:', kwargs)
        result = func(*args, **kwargs)
        print('Result:', result)
        return result
    return new_function

#def add_ints(a, b):
#    return a + b
#cooler_add_ints = document_it(add_ints)
#cooler_add_ints(3, 5)
#('Running function:', 'add_ints')
#('Positional arguments:', (3, 5))
#('Keyword arguments:', {})
#('Result:', 8)

#@document_it
#def add_ints(a, b):
#    return a + b

#add_ints(3, 5)

def square_it(func):
    def new_function(*args, **kwargs):
        result = func(*args, **kwargs)
        return result * result
    return new_function

#@square_it
#@document_it
#def add_ints(a, b):
#    return a + b

#add_ints(3, 5)

#('Running function:', 'add_ints')
#('Positional arguments:', (3, 5))
#('Keyword arguments:', {})
#('Result:', 8)

@document_it
@square_it
def add_ints(a, b):
    return a + b

add_ints(3, 5)

#('Running function:', 'new_function')
#('Positional arguments:', (3, 5))
#('Keyword arguments:', {})
#('Result:', 64)

#靠近函数定义的装饰器最先执行

def log(func):
    def wrapper(*args, **kw):
        print('call %s():' % func.__name__)
        return func(*args, **kw)
    return wrapper

@log
def now():
    print('2015-3-25')

now()

#call now():
#2015-3-25

如果decorator本身需要传入参数

def log(text):
    def decorator(func):
        def wrapper(*args, **kw):
            print('%s %s():' % (text, func.__name__))
            return func(*args, **kw)
        return wrapper
    return decorator

@log('execute')
def now():
    print('2015-3-25')

now()

print(now.__name__)

#execute now():
#2015-3-25
#wrapper

不需要编写wrapper.__name__ = func.__name__这样的代码，Python内置的functools.wraps就是干这个事的

相当于：

now = log(now)
now = log('execute')(now)