def from_geom(geom):
        """
        Create and return a position object for the geom

        Parameters
        ----------
        geom : geom
            An instantiated geom object.

        Returns
        -------
        out : position
            A position object

        Raises :class:`PlotnineError` if unable to create a `position`.
        """
        name = geom.params['position']
        if issubclass(type(name), position):
            return name

        if isinstance(name, type) and issubclass(name, position):
            klass = name
        elif is_string(name):
            if not name.startswith('position_'):
                name = 'position_{}'.format(name)
            klass = Registry[name]
        else:
            raise PlotnineError(
                'Unknown position of type {}'.format(type(name)))

        return klass()
Create and return a position object for the geom

        Parameters
        ----------
        geom : geom
            An instantiated geom object.

        Returns
        -------
        out : position
            A position object

        Raises :class:`PlotnineError` if unable to create a `position`.