Python class and instance methods that can share a name

dualmethod.py

# coding: utf-8


"""Instance and class methods that can share a name"""


class DualMethod(object):
    """A method that can be called as instance method and as class method
    
    >>> class Test(object):
    ...
    ...     @dualmethod
    ...     def spam(self):
    ...         print "I am an instance method"
    ...
    ...     @spam.classmethod
    ...     def spam(cls):
    ...         print "I am a class method"
    ...
    ...
    >>> Test.spam()
    I am a class method
    >>> Test().spam()
    I am an instance method
    
    """

    def __init__(self, instancemethod, classmethod=None):
        self.instancemethod = instancemethod
        self._classmethod = classmethod

    def __get__(self, obj, type=None):
        """
        Return instancemethod if there is an instance. If there is no instance
        and there is a type, return classmethod instead
        """
        if obj:
            return self.instancemethod.__get__(obj)
        if type:
            return self._classmethod.__get__(type)
        raise TypeError("Invalid dualmethod")

    def classmethod(self, func):
        "setter for class methods"
        self._classmethod = func
        return self


def dualmethod(func):
    "Convenient decorator"
    return DualMethod(func)


if __name__ == "__main__":

    import unittest

    class DualMethodTestCase(unittest.TestCase):

        def test_dualmethod(self):

            class Test(object):

                @dualmethod
                def spam(self):
                    return self

                @spam.classmethod
                def spam(cls):
                    return cls

            instance = Test()

            self.assertIs(instance.spam(), instance)
            self.assertIs(Test.spam(), Test)


    unittest.main()