python

Question

我正在尝试根据这篇文章 http://www.artima.com/weblogs/viewpost.jsp?thread=101605 实现一种多方法方法。这种方法有两个不同之处：

我只需要看multimethod的第一个参数，所以不需要形成arg的元组classes
多方法将存在于 classes 中，它们将不是常规函数。

但是我有点混淆了我的 classes，并且在调度对 class 方法的调用时，对 self 的调用丢失了。

这是我的代码：

method_registry = {}


class SendMessageMultiMethod(object):
    """
    A class for implementing multimethod functionality
    """
    def __init__(self, name):
        self.name = name
        self.typemap = {}

    def __call__(self, message, extra_payload=None):
        """
        Overrriding method call and dispatching it to an actual method
        based on the supplied message class
        """
        first_arg_type = message.__class__
        function = self.typemap.get(first_arg_type)
        print(
            'Dispatching to function {} with message {} and extra payload {}...'
            .format(function, message, extra_payload)
        )
        return function(message, extra_payload)

    def register(self, type_, function):
        self.typemap[type_] = function


def use_for_type(*types):
    """
    A decorator that registers a method to use with certain types
    """

    def register(method):
        """Creating Multimethod with the method name
        and registering it at at method_registry dict """
        name = method.__name__
        mm = method_registry.get(name)
        if mm is None:
            mm = method_registry[name] = SendMessageMultiMethod(name)
        for type_ in types:
            mm.register(type_, method)
        return mm

    return register


class Sender(object):

    def send_messages(self, messages_list):
        for message in messages_list:
            # this is supposed to fire different send_message() methods
            # for different arg types
            self.send_message(message)

    @use_for_type(int, float)
    def send_message(self, message, *args, **kwargs):
        print('received call for int/float message {} with {}, {}'
              .format(message, args, kwargs))
        print('self is {}'.format(self))

    @use_for_type(bool)
    def send_message(self, message, *args, **kwargs):
        print('received call for bool message {} with {}, {}'
              .format(message, args, kwargs))
        print('self is {}'.format(self))

因此，当我在 Sender class 上调用 send_messages 方法时，我收到 self 中的参数，而不是 message 变量中的参数。这里：

sender = Sender()
sender.send_messages([1, 2, True, 5.6])

输出：

Dispatching to function <function Sender.send_message at 0x1013608c8> with message 1 and extra payload None...
received call for int/float message None with (), {}
self is 1
Dispatching to function <function Sender.send_message at 0x1013608c8> with message 2 and extra payload None...
received call for int/float message None with (), {}
self is 2
Dispatching to function <function Sender.send_message at 0x101360950> with message True and extra payload None...
received call for bool message None with (), {}
self is True
Dispatching to function <function Sender.send_message at 0x1013608c8> with message 5.6 and extra payload None...
received call for int/float message None with (), {}
self is 5.6

如何不丢失 self 并将消息内容分派给 message 变量？

Answer 1

正如 Python 方法签名（如 def send_message(self, message, *args, **kwargs) 所建议的那样，方法的第一个参数必须是 self 对象。通常，通过执行 obj.send_message，您可以访问 对象的 方法，而不是 classes'。尝试以下操作：

>>> class Foo():
...     def bar(self):
...         pass

>>> Foo.bar
<function __main__.Foo.bar>

>>> Foo().bar
<bound method Foo.bar of <__main__.Foo object at 0x7f5fd927cc18>>

绑定方法表示已经指定了self。

您的 @use_for_type 装饰器在 class 级别工作，所以在您的 send_message 函数上工作，而不是绑定方法。

现在它只是找出您的代码在哪里缺少显式传递 self，这是 __call__ 中的一件事 - self 是 SendMessageMultiMethod 对象，不是 Sender 对象 - 在你的装饰器中：

class SendMessageMultiMethod(object):
    ...

    # note the `self_` parameter
    def __call__(self, self_, message, extra_payload=None):
        ...
        return function(self_, message, extra_payload)


def use_for_type(*types):
    ...

    def register(method):
        ...

        return lambda self, *args, **kwargs: mm(self, *args, **kwargs)

输出：

Dispatching to function <function Sender.send_message at 0x7f1e427e5488> with message 1 and extra payload None...
received call for int/float message 1 with (None,), {}
self is <__main__.Sender object at 0x7f1e4277b0f0>
Dispatching to function <function Sender.send_message at 0x7f1e427e5488> with message 2 and extra payload None...
received call for int/float message 2 with (None,), {}
self is <__main__.Sender object at 0x7f1e4277b0f0>
Dispatching to function <function Sender.send_message at 0x7f1e427e5598> with message True and extra payload None...
received call for bool message True with (None,), {}
self is <__main__.Sender object at 0x7f1e4277b0f0>
Dispatching to function <function Sender.send_message at 0x7f1e427e5488> with message 5.6 and extra payload None...
received call for int/float message 5.6 with (None,), {}
self is <__main__.Sender object at 0x7f1e4277b0f0>

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