'Replace the contains test used by this artist. The new picker
should be a callable function which determines whether the
artist is hit by the mouse event::
hit, props = picker(artist, mouseevent)
If the mouse event is over the artist, return *hit* = *True*
and *props* is a dictionary of properties you want returned
with the contains test.
ACCEPTS: a callable function'

def set_contains(self, picker):

    self._contains = picker
