Python decorator

#!python2
#-*- coding:utf-8 -*-



def f():
    print "Call function f"
    
f1=f
f1()

#查看函数对象的名字
f.__name__
f1.__name__

#导入functools模块
#因为经过装饰的函数它们的__name__变成了decorator里面的函数名字，对于
#这个例子就是write_ahead
#为了把原始函数名字等属性复制到write_ahead中我们使用@functools.wraps(func)
#这样就可以避免类似write_ahead.__name__ = func.__name__的代码


import functools

#定义一个decorator，接受函数f为参数

def log(func):
    @functools.wraps(func)
    def write_ahead(*args,**kw):
        print "Will Call %s" % f.__name__
        func(*args,**kw)
        print "After call func:"
        
    return write_ahead

#用@把decorator置于函数f定义处

@log
def f():
    print "Call function f"

f1=f
f.__name__
f1.__name__

#调用函数f不仅会调用f本身还会在其前后打印log
#相当于 f=log(f)

f1()



#下面是接受参数的decorator写法


import functools

def log(text):
    def decorator(func):
        @functools.wraps(func)
        def write_ahead(*args,**kw):
            print "Will Call %s with %s" % (f.__name__,text)
            func(*args,**kw)
            print "After call func:"
        return write_ahead
    return decorator

@log("sss")
def f():
    print "Call function f"

f1=f
f.__name__
f1.__name__
f1()



#把以上俩种整合

def log(obj):
    
    if isinstance(obj,str):
        
        text=obj
        
        def decorator(func):
            @functools.wraps(func)
            def write_ahead(*args,**kw):
                print "Will Call %s with %s" % (f.__name__,text)
                func(*args,**kw)
                print "After call func:"
            return write_ahead
        return decorator
    
    else:
        
        func=obj
        @functools.wraps(func)
        def write_ahead(*args,**kw):
            print "Will Call %s" % f.__name__
            func(*args,**kw)
            print "After call func:"
        return write_ahead
        
@log
def f():
    print "Call function f"

f1=f
f.__name__
f1.__name__
f1()


@log("sss")
def f():
    print "Call function f"

f1=f
f.__name__
f1.__name__
f1()

#class decorator

class c_d(object):
    def __init__(self,func):
        self._func=func
        
    def __call__(self):
        print "class decorator is running"
        self._func()
        print "class decorator is ending"
        
@c_d

def test():
    print "call test func"
    
test()

#装饰器顺序

@a
@b
@c

def f():
    
等价于

f=a(b(c(f)))