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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def copy_mode(pymux, variables):
 """ Enter copy mode. """

    go_up = variables['-u']  # Go in copy mode and page-up directly.
    # TODO: handle '-u'

    pane = pymux.arrangement.get_active_pane()
    pane.enter_copy_mode()