'Add a binding to each ``Tkinter.Label`` and ``Tkinter.Listbox``
widget in this mult-column listbox that will call ``func`` in
response to the event sequence.
:return: A list of the identifiers of replaced binding
functions (if any), allowing for their deletion (to
prevent a memory leak).'

def bind_to_columns(self, sequence=None, func=None, add=None):

    return (self.bind_to_labels(sequence, func, add) + self.bind_to_listboxes(sequence, func, add))
