你也可以使用__call__方法来实现装饰器。

这个例子来自Python 3模式，食谱和习语

class decorator_without_arguments(object):
    def __init__(self, f):
        """
        If there are no decorator arguments, the function
        to be decorated is passed to the constructor.
        """
        print("Inside __init__()")
        self.f = f

    def __call__(self, *args):
        """
        The __call__ method is not called until the
        decorated function is called.
        """
        print("Inside __call__()")
        self.f(*args)
        print("After self.f( * args)")


@decorator_without_arguments
def sayHello(a1, a2, a3, a4):
    print('sayHello arguments:', a1, a2, a3, a4)


print("After decoration")
print("Preparing to call sayHello()")
sayHello("say", "hello", "argument", "list")
print("After first sayHello() call")
sayHello("a", "different", "set of", "arguments")
print("After second sayHello() call")

输出:

__init__将被视为构造函数，其中__call__方法可以被对象调用任意次数。__init__和__call__函数都接受默认参数。

定义自定义__call__()方法允许将类的实例作为函数调用，而不总是修改实例本身。

In [1]: class A:
   ...:     def __init__(self):
   ...:         print "init"
   ...:         
   ...:     def __call__(self):
   ...:         print "call"
   ...:         
   ...:         

In [2]: a = A()
init

In [3]: a()
call

__call__允许返回任意值，而__init__作为构造函数隐式返回类的实例。正如其他答案正确指出的那样，__init__只被调用一次，而__call__有可能被调用多次，以防初始化的实例被赋值给中间变量。

>>> class Test:
...     def __init__(self):
...         return 'Hello'
... 
>>> Test()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: __init__() should return None, not 'str'
>>> class Test2:
...     def __call__(self):
...         return 'Hello'
... 
>>> Test2()()
'Hello'
>>> 
>>> Test2()()
'Hello'
>>> 

案例1:

class Example:
    def __init__(self, a, b, c):
        self.a=a
        self.b=b
        self.c=c
        print("init", self.a, self.b, self.c)

Run:

Example(1,2,3)(7,8,9)

结果:

- init 1 2 3
- TypeError: 'Example' object is not callable

案例2:

class Example:
    def __init__(self, a, b, c):
        self.a=a
        self.b=b
        self.c=c
        print("init", self.a, self.b, self.c)
    def __call__(self, x, y, z):
        self.x=x
        self.y=y
        self.z=z
        print("call", self.x, self.y, self.z)

Run:

Example(1,2,3)(7,8,9)

结果:

- init 1 2 3
- call 7 8 9

你也可以使用__call__方法来实现装饰器。

这个例子来自Python 3模式，食谱和习语

class decorator_without_arguments(object):
    def __init__(self, f):
        """
        If there are no decorator arguments, the function
        to be decorated is passed to the constructor.
        """
        print("Inside __init__()")
        self.f = f

    def __call__(self, *args):
        """
        The __call__ method is not called until the
        decorated function is called.
        """
        print("Inside __call__()")
        self.f(*args)
        print("After self.f( * args)")


@decorator_without_arguments
def sayHello(a1, a2, a3, a4):
    print('sayHello arguments:', a1, a2, a3, a4)


print("After decoration")
print("Preparing to call sayHello()")
sayHello("say", "hello", "argument", "list")
print("After first sayHello() call")
sayHello("a", "different", "set of", "arguments")
print("After second sayHello() call")

输出: