object.__call__(self[, args...])

Called when the instance is “called” as a function; if this method is defined, x(arg1, arg2, ...) is a shorthand for x.__call__(arg1, arg2, ...).

Python中有一个有趣的语法，只要定义类型的时候，实现__call__函数，这个类型就成为可调用的。换句话说，我们可以把这个类的对象当作函数来使用，相当于重载了括号运算符。

class Student(object):

    def __init__(self, name):

        self.name = name

    def __call__(self):

        print('My name is %s.' % self.name)

s = Student('Michael')

s()

# My name is Michael.

---

通过使用__setattr__, __getattr__, __delattr__可以重写dict,使之通过“.”调用键值。

class Dict(dict):

    '''

    通过使用__setattr__,__getattr__,__delattr__

    可以重写dict,使之通过“.”调用

    '''

    def __setattr__(self, key, value):

        print("In '__setattr__")

        self[key] = value

    def __getattr__(self, key):

        try:

            print("In '__getattr__")

            return self[key]

        except KeyError as k:

            return None

    def __delattr__(self, key):

        try:

            del self[key]

        except KeyError as k:

            return None

    # __call__方法用于实例自身的调用,达到()调用的效果

    def __call__(self, key):    # 带参数key的__call__方法

        try:

            print("In '__call__'")

            return self[key]

        except KeyError as k:

            return "In '__call__' error"

s = Dict()

print(s.__dict__)

# {}

s.name = "hello"    # 调用__setattr__

# In '__setattr__

print(s.__dict__) # 由于调用的'__setattr__', name属性没有加入实例属性字典中。

# {}

print(s("name"))    # 调用__call__

# In '__call__'

# hello

print(s["name"])    # dict默认行为

# hello

# print(s)

print(s.name)       # 调用__getattr__

# In '__getattr__

# hello

del s.name          # 调用__delattr__

print(s("name"))    # 调用__call__

# None