Creating dynamic attributes in Python via overriding "__getattr__" and "__setattr__" magic methods

dynamic_attributes.py

# Illustrates creating dynamic attributes in Python
#
# For implementation details of the dynamic attributes, please see the following methods:
#  - GPSPosition.__getattr__
#  - GPSPosition.__setattr__
#

class GPSPosition(object):
    __slots__ = ('_coords', '_attribs', '_iter_index')

    def __init__(self, coords, **kwargs):
        self._coords = coords
        self._attribs = kwargs.get('attribs', tuple())

    def __str__(self):
        return str(self._coords)

    def __repr__(self):
        return self.__str__()

    def __iter__(self):
        self._iter_index = 0
        return self

    def next(self):
        return self.__next__()

    def __next__(self):
        try:
            res = self._coords[self._iter_index]
        except IndexError:
            raise StopIteration
        self._iter_index += 1
        return res

    def __len__(self):
        return len(self._coords)

    def __reversed__(self):
        return reversed(self._coords)

    def __getitem__(self, key):
        return self._coords[key]

    def __setitem__(self, key, value):
        self._coords[key] = value

    def __getattr__(self, name):
        try:
            # Try to get the attribute name from the attribute list
            # 'index' function will return the index of the attribute in the '_attribs' list
            idx = object.__getattribute__(self, '_attribs').index(name)
            # Since we know the index value, it should be the same in the '_coords' list
            return object.__getattribute__(self, '_coords')[idx]
        except ValueError:
            # 'index' function will throw a 'ValueError' exception if 'attr' is not in the list
            raise AttributeError("'" + self.__class__.__name__ + "' object has no attribute '" + name + "'")
        except AttributeError:
            return object.__getattribute__(self, name)

    def __setattr__(self, name, value):
        # Check if the 'name' is in the '__slots__'
        if name in object.__getattribute__(self, '__slots__'):
            object.__setattr__(self, name, value)
        else:
            try:
                # Try to get the attribute name from the attribute list
                # 'index' function will return the index of the attribute in the '_attribs' list
                idx = object.__getattribute__(self, '_attribs').index(name)
                # Get the '_coords' list
                temp = object.__getattribute__(self, '_coords')
                # Update the '_coords' list
                temp[idx] = value
                # Update the class member in this instance
                object.__setattr__(self, '_coords', temp)
            except ValueError:
                # 'index' function will throw a 'ValueError' exception if 'name' is not in the list
                raise AttributeError("'" + self.__class__.__name__ + "' object has no attribute '" + name + "'")

    @property
    def coordinates(self):
        return self._coords

    @coordinates.setter
    def coordinates(self, val):
        if not isinstance(val, (list, tuple)):
            raise TypeError("Input for 'coordinates' should be a list or tuple")
        self._coords = list(val)

    @property
    def attributes(self):
        return self._attribs

    @attributes.setter
    def attributes(self, val):
        if not isinstance(val, (list, tuple)):
            raise TypeError("Input for 'attributes' should be a list or tuple")
        self._attribs = tuple(val)


# Example run
if __name__ == '__main__':
    # Create a 3-D GPSPosition instance and set the coordinates & attributes
    pos1 = GPSPosition([10, 21, 32], attribs=['x', 'y', 'z'])

    # Print 'position'
    print('pos1:', pos1)

    # Get dynamic properties
    print('x:', pos1.x)  # will print 10
    print('y:', pos1.y)  # will print 21
    print('z:', pos1.z)  # will print 32

    # Set dynamic properties
    pos1.x = 12
    print('updated x:', pos1.x)  # will print 12

    # Create a 4-D GPSPosition instance and set the coordinates & attributes
    pos2 = GPSPosition([11, 13, 17, 19], attribs=['x', 'y', 'z', 'w'])

    # Print 'position'
    print('pos2:', pos2)

    # Get dynamic properties
    print('x:', pos2.x)  # will print 11
    print('y:', pos2.y)  # will print 13
    print('z:', pos2.z)  # will print 17
    print('w:', pos2.w)  # will print 19

    # Set dynamic properties
    pos2.w = 23
    print('updated w:', pos2.w)  # will print 23

    # Create a 2-D GPSPosition instance and set the coordinates & attributes
    pos3 = GPSPosition([100, 200], attribs=['u', 'v'])

    # Print 'position'
    print('pos3:', pos3)

    # Get dynamic properties
    print('u:', pos3.u)  # will print 100
    print('v:', pos3.v)  # will print 200

    # Set dynamic properties
    pos3.u = 150
    pos3.v = 250
    print('updated u:', pos3.u)  # will print 150
    print('updated v:', pos3.v)  # will print 250

    # Create a 2-D GPSPosition instance without the attributes
    pos4 = GPSPosition([36, 42])

    # Print 'position'
    print('pos4:', pos4)