'Add a rotation (in radians) around the point (x, y) in place.
Returns *self*, so this method can easily be chained with more
calls to :meth:`rotate`, :meth:`rotate_deg`, :meth:`translate`
and :meth:`scale`.'

def rotate_around(self, x, y, theta):

    return self.translate((- x), (- y)).rotate(theta).translate(x, y)
