def from_list(cls, l):
        """Return a Point instance from a given list"""
        if len(l) == 3:
                x, y, z = map(float, l)
                return cls(x, y, z)
        elif len(l) == 2:
            x, y = map(float, l)
            return cls(x, y)
        else:
            raise AttributeError
Return a Point instance from a given list