Unpacking property example

unpacking_property.py

from weakref import WeakKeyDictionary

class TupleProperty:
    def __init__(self, *default_value):
        self.values = WeakKeyDictionary()
        self.length = len(default_value)
        self.default_value = default_value

    def __get__(self, obj, cls=None):
        if obj:
            return self.values.get(obj, self.default_value)
        else:
            return self

    def __set__(self, obj, value):
        assert len(value) == self.length
        self.values[obj] = tuple(value)

    def __iter__(self):
        for i in range(self.length):
            yield ComponentProperty(self, i)


class ComponentProperty:
    def __init__(self, parent, index):
        self.parent = parent
        self.index = index

    def __get__(self, obj, cls=None):
        if obj:
            return self.parent.__get__(obj)[self.index]
        else:
            return self

    def __set__(self, obj, value):
        prev = self.parent.__get__(obj)
        new_tuple = prev[:self.index] + (value, ) + prev[self.index + 1:]
        self.parent.__set__(obj, new_tuple)


def test_prop():
    class SomeObject:
        position = x, y, z = TupleProperty(0, 0, 0)

    obj = SomeObject()
    assert obj.position == (0, 0, 0)
    assert obj.x == obj.y == obj.z == 0
    obj.x = 1
    assert obj.position == (1, 0, 0)
    obj.y = 2
    assert obj.position == (1, 2, 0)
    obj.position = 4, 5, 6
    assert obj.x == 4
    assert obj.y == 5
    assert obj.z == 6

if __name__ == '__main__':
    test_prop()