注册器机制的引入是为了使工程的扩展性变得更好。当产品增加某个功能需要增加一些新函数或者类时，它可以保证我们可以复用之前的逻辑。
我们来看一下它的使用方法：

register_obj = RegisterMachine("register")
# decorate method
@register_obj.register()
def say_hello_with(name):
    print("Hello, {person}!".format(person=name))
    
def say_hi_with(name):
    print("Hi, {person}!".format(person=name))
    
register_obj.get("say_hello_with")("Peter")
# function call method
register_obj.register(say_hi_with)
register_obj.get("say_hi_with")("John")

从上面的例子我们可以看出，我们通过register_obj这个对象，通过传入对应的函数名来得到该函数。接下来介绍下具体的实现：

class RegisterMachine(object):
    def __init__(self, name):
        # name of register
        self._name = name
        self._name_method_map = dict()
    
    def register(self, obj=None):
        # obj == None for function call register
        # otherwise for decorator way
        if obj != None:
            name = obj.__name__
            self._name_method_map[name] = obj
        
        else:
            def wrapper(func):
                name = func.__name__
                self._name_method_map[name] = func
                return func
            return wrapper

    def get(self, name):
        return self._name_method_map[name]

if __name__ == "__main__":
    register_obj = RegisterMachine("register")
    # decorate method
    @register_obj.register()
    def say_hello_with(name):
        print("Hello, {person}!".format(person=name))

    def say_hi_with(name):
        print("Hi, {person}!".format(person=name))

    register_obj.get("say_hello_with")("Peter")
    # function call method
    register_obj.register(say_hi_with)
    register_obj.get("say_hi_with")("John")