Ruby在Python中的"method_missing"

问题描述

Python中是否有诸如Ruby中的method_missing技术之类的用于拦截消息(方法调用)的技术?

Is there any technique available in Python for intercepting messages (method calls) like the method_missing technique in Ruby?

推荐答案

正如其他人所提到的，在Python中，当您执行o.f(x)时，它实际上是一个两步操作:首先，获取f属性o，然后使用参数x调用它.因为没有属性f，所以第一步失败了，而这是调用Python魔术方法__getattr__的那一步.

As others have mentioned, in Python, when you execute o.f(x), it's really a two-step operation: First, get the f attribute of o, then call it with parameter x. It's the first step that fails because there is no attribute f, and it's that step that invokes the Python magic method __getattr__.

因此您必须实现__getattr__，并且它返回的内容必须是可调用的.请记住，如果您还尝试获取o.some_data_that_doesnt_exist，则将调用相同的__getattr__，并且它不会知道它是数据"属性还是正在寻找的方法".

So you have to implement __getattr__, and what it returns must be callable. Keep in mind, if you also try to get o.some_data_that_doesnt_exist, the same __getattr__ will be called, and it won't know that it's a "data" attribute vs. a "method" that being sought.

以下是返回可调用对象的示例:

Here's an example of returning a callable:

class MyRubylikeThing(object):
    #...

    def __getattr__(self, name):
        def _missing(*args, **kwargs):
            print "A missing method was called."
            print "The object was %r, the method was %r. " % (self, name)
            print "It was called with %r and %r as arguments" % (args, kwargs)
        return _missing

r = MyRubylikeThing()
r.hello("there", "world", also="bye")

产生:

A missing method was called.
The object was <__main__.MyRubylikeThing object at 0x01FA5940>, the method was 'hello'.
It was called with ('there', 'world') and {'also': 'bye'} as arguments

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