How can I make an alias to a non-function member attribute in a Python class?

Question

I\'m in the midst of writing a Python library API and I often run into the scenario where my users want multiple different names for the same functions and variables.

If

Answer 1

You could use some of ideas shown in the ActiveState Python recipe titled Caching and aliasing with descriptors. Here's a concise version of the code shown there which provides the functionality you seek.

Edit: A class containing Alias attributes could be made to automatically delete any associated target attributes when you del one (and vice-versa). The code for my answer now illustrates one easy way this could be done using a convenient class decorator which adds a custom __delattr__() to do the specialized deletion management when attribute Alias's could be involved.

class Alias(object):
    """ Descriptor to give an attribute another name. """
    def __init__(self, name):
        self.name = name
    def __get__(self, inst, cls):
        if inst is None:
            return self  # a class attribute reference, return this descriptor
        return getattr(inst, self.name)
    def __set__(self, inst, value):
        setattr(inst, self.name, value)
    def __delete__(self, inst):
        delattr(inst, self.name)


def AliasDelManager(cls):
    """ Class decorator to auto-manage associated Aliases on deletion. """
    def __delattr__(self, name):
        """ Deletes any Aliases associated with a named attribute, or
            if attribute is itself an Alias, deletes the associated target.
        """
        super(cls, self).__delattr__(name) # Use base class' method.
        for attrname in dir(self):
            attr = getattr(cls, attrname)
            if isinstance(attr, Alias) and attr.name == name:
                delattr(cls, attrname)

    setattr(cls, '__delattr__', __delattr__)
    return cls


if __name__=='__main__':
    @AliasDelManager
    class Dummy(object):
        def __init__(self):
            self.x = 17
        xValue = Alias('x')  # create an Alias for attr 'x'

    d = Dummy()
    assert d.x == 17
    assert d.xValue == 17
    d.x = 23
    assert d.xValue == 23
    d.xValue = 1492
    assert d.x == 1492
    assert d.x is d.xValue
    del d.x  # should also remove any associated Aliases
    assert 'xValue' not in dir(d)
    print('done - no exceptions were raised')