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    <p>I recently encountered the same problem. That is, I needed abstract classmethods but was unable to use Python 3 because of other project constraints. The solution I came up with is the following.</p> <p>abcExtend.py:</p> <pre><code>import abc class instancemethodwrapper(object): def __init__(self, callable): self.callable = callable self.__dontcall__ = False def __getattr__(self, key): return getattr(self.callable, key) def __call__(self, *args, **kwargs): if self.__dontcall__: raise TypeError('Attempted to call abstract method.') return self.callable(*args,**kwargs) class newclassmethod(classmethod): def __init__(self, func): super(newclassmethod, self).__init__(func) isabstractmethod = getattr(func,'__isabstractmethod__',False) if isabstractmethod: self.__isabstractmethod__ = isabstractmethod def __get__(self, instance, owner): result = instancemethodwrapper(super(newclassmethod, self).__get__(instance, owner)) isabstractmethod = getattr(self,'__isabstractmethod__',False) if isabstractmethod: result.__isabstractmethod__ = isabstractmethod abstractmethods = getattr(owner,'__abstractmethods__',None) if abstractmethods and result.__name__ in abstractmethods: result.__dontcall__ = True return result class abstractclassmethod(newclassmethod): def __init__(self, func): func = abc.abstractmethod(func) super(abstractclassmethod,self).__init__(func) </code></pre> <p>Usage:</p> <pre><code>from abcExtend import abstractclassmethod class A(object): __metaclass__ = abc.ABCMeta @abstractclassmethod def foo(cls): return 6 class B(A): pass class C(B): @classmethod def foo(cls): return super(C,cls).foo() + 1 try: a = A() except TypeError: print 'Instantiating A raises a TypeError.' try: A.foo() except TypeError: print 'Calling A.foo raises a TypeError.' try: b = B() except TypeError: print 'Instantiating B also raises a TypeError because foo was not overridden.' try: B.foo() except TypeError: print 'As does calling B.foo.' #But C can be instantiated because C overrides foo c = C() #And C.foo can be called print C.foo() </code></pre> <p>And here are some pyunit tests which give a more exhaustive demonstration.</p> <p>testAbcExtend.py:</p> <pre><code>import unittest import abc oldclassmethod = classmethod from abcExtend import newclassmethod as classmethod, abstractclassmethod class Test(unittest.TestCase): def setUp(self): pass def tearDown(self): pass def testClassmethod(self): class A(object): __metaclass__ = abc.ABCMeta @classmethod @abc.abstractmethod def foo(cls): return 6 class B(A): @classmethod def bar(cls): return 5 class C(B): @classmethod def foo(cls): return super(C,cls).foo() + 1 self.assertRaises(TypeError,A.foo) self.assertRaises(TypeError,A) self.assertRaises(TypeError,B) self.assertRaises(TypeError,B.foo) self.assertEqual(B.bar(),5) self.assertEqual(C.bar(),5) self.assertEqual(C.foo(),7) def testAbstractclassmethod(self): class A(object): __metaclass__ = abc.ABCMeta @abstractclassmethod def foo(cls): return 6 class B(A): pass class C(B): @oldclassmethod def foo(cls): return super(C,cls).foo() + 1 self.assertRaises(TypeError,A.foo) self.assertRaises(TypeError,A) self.assertRaises(TypeError,B) self.assertRaises(TypeError,B.foo) self.assertEqual(C.foo(),7) c = C() self.assertEqual(c.foo(),7) if __name__ == "__main__": #import sys;sys.argv = ['', 'Test.testName'] unittest.main() </code></pre> <p>I haven't evaluated the performance cost of this solution, but it has worked for my purposes so far.</p>
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