在 Python 中调用超类的类方法 [英] Invoking a superclass's class methods in Python

问题描述

我正在为 Flask 添加 CouchDB 支持的 Flask 扩展.为方便起见，我对 couchdb.mapping.Document 进行了子类化，以便 store 和 load 方法可以使用当前线程本地数据库.现在，我的代码如下所示:

I am working on a Flask extension that adds CouchDB support to Flask. To make it easier, I have subclassed couchdb.mapping.Document so the store and load methods can use the current thread-local database. Right now, my code looks like this:

class Document(mapping.Document):
  # rest of the methods omitted for brevity
  @classmethod
  def load(cls, id, db=None):
    return mapping.Document.load(cls, db or g.couch, id)

为简洁起见，我省略了一些，但这是重要的部分.但是，由于 classmethod 的工作方式，当我尝试调用此方法时，收到错误消息

I left out some for brevity, but that's the important part. However, due to the way classmethod works, when I try to call this method, I receive the error message

  File "flaskext/couchdb.py", line 187, in load
    return mapping.Document.load(cls, db or g.couch, id)
TypeError: load() takes exactly 3 arguments (4 given)

我测试了用 mapping.Document.load.im_func(cls, db or g.couch, id) 替换调用，它有效，但我对访问内部不是特别满意im_ 属性(即使它们被记录在案).有没有人有更优雅的方法来处理这个问题?

I tested replacing the call with mapping.Document.load.im_func(cls, db or g.couch, id), and it works, but I'm not particularly happy about accessing the internal im_ attributes (even though they are documented). Does anyone have a more elegant way to handle this?

推荐答案

我认为您实际上需要在这里使用 super.无论如何，这是调用超类方法的更简洁的方法:

I think you actually need to use super here. That's the neater way to call superclass methods anyway:

class A(object):
    @classmethod
    def load(cls):
        return cls

class B(A):
    @classmethod
    def load(cls):
        # return A.load() would simply do "A.load()" and thus return a A
        return super(B, cls).load() # super figures out how to do it right ;-)


print B.load()

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