'Add a binding to each ``Tkinter.Label`` 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_labels(self, sequence=None, func=None, add=None):

    return [label.bind(sequence, func, add) for label in self.column_labels]
