2

我有一些代码，我想交替传递实例或类。我在该代码中要做的就是调用一个我希望类和实例都具有的方法（go()下面示例中的方法）。

不幸的是，我不能创建一个与常规方法同名的类方法......见下面的例子。我最初预计第二次调用会产生一个a而不是一个b.

关于如何实现这一目标的任何建议？

Type "help", "copyright", "credits" or "license" for more information.
>>> class A(object):
...     def go(self):
...             print "a"
...     @classmethod
...     def go(cls):
...             print "b"
... 
>>> a=A()
>>> a.go()
b
>>> A.go()
b
4

3 回答 3

4

您可以使用特制__get__()方法创建自己的方法类型。

在这种方法中，您可以执行以下操作：

class combimethod(object):
    def __init__(self, func):
        self._func = func
    def classmethod(self, func):
        self._classfunc = classmethod(func)
        return self
    def __get__(self, instance, owner):
        if instance is None:
            return self._classfunc.__get__(instance, owner)
        else:
            return self._func.__get__(instance, owner)

class A(object):
    @combimethod
    def go(self):
        print "instance", self
    @go.classmethod
    def go(cls):
        print "class", cls

a=A()
print "i:",
a.go()
print "c:",
A.go()

注意：上面的测试不是很彻底，但似乎有效。尽管如此，它应该被视为一种“接近解决方案的伪代码”，而不是一种解决方案。它应该让你知道如何实现你的目标。

于 2012-05-02T12:18:59.277 回答
3

考虑重用classinstancemethod来自formencode 的装饰器。

https://bitbucket.org/formencode/official-formencode/src/06d52c5b33c9/formencode/declarative.py

class classinstancemethod(object):
    """
    Acts like a class method when called from a class, like an
    instance method when called by an instance.  The method should
    take two arguments, 'self' and 'cls'; one of these will be None
    depending on how the method was called.
    """

    def __init__(self, func):
        self.func = func

    def __get__(self, obj, type=None):
        return _methodwrapper(self.func, obj=obj, type=type)


class _methodwrapper(object):

    def __init__(self, func, obj, type):
        self.func = func
        self.obj = obj
        self.type = type

    def __call__(self, *args, **kw):
        assert 'self' not in kw and 'cls' not in kw, (
            "You cannot use 'self' or 'cls' arguments to a "
            "classinstancemethod")
        return self.func(*((self.obj, self.type) + args), **kw)

    def __repr__(self):
        if self.obj is None:
            return ('<bound class method %s.%s>'
                    % (self.type.__name__, self.func.func_name))
        else:
            return ('<bound method %s.%s of %r>'
                    % (self.type.__name__, self.func.func_name, self.obj))
于 2012-05-02T12:29:09.957 回答
1

怎么样：

import inspect

class A(object):
   @staticmethod
   def go(obj):
      if inspect.isclass(obj):
         print 'class'
      else:
         print 'instance'

A.go(int) # class
A.go(1)   # instance
A.go(A)   # class
A.go(A()) # instance
于 2012-05-02T12:14:15.753 回答