def get_top_fitness(dirty_values):
    """Return top fitness value.

    Returns the top fitness values of a
    :class:`~paddy.Paddy_Runner.PFARunner`, solely, for each iteration as a
    list when passed a dictionary with the structure type of
    :attr:`~paddy.Paddy_Runner.PFARunner.top_values`.

    Parameters
    ----------
    dirty_values : dictionary
        A dictionary in the form of :attr:`~PFARunner.top_values`.

    Returns
    -------
    fitness_list : list of floats
        A list of the top fitness value evaluated for sowing during each
        itteration.

    See Also
    --------
    :meth:`paddy.Paddy_Runner.PFARunner.run_paddy`

    Notes
    -----
    The top value evaluated for sowing when using 'population' for
    the `paddy_type` parameter of a `PFARunner` instance might not be the
    value of a seed generated during that itteration.  See (need to find home for the full description of the PFA)

    """
    fitness_list = []
    for i in dirty_values:
        fitness_list.append(dirty_values[i]['fitness'])
    return fitness_list
