Plot a diagram

def plot(values, mode_names, title, (xlabel, ylabel), out_file):
    """Plot a diagram"""
    matplotlib.pyplot.clf()
    for mode, mode_name in mode_names.iteritems():
        vals = values[mode]
        matplotlib.pyplot.plot(
            [x for x, _ in vals],
            [y for _, y in vals],
            label=mode_name
        )
    matplotlib.pyplot.title(title)
    matplotlib.pyplot.xlabel(xlabel)
    matplotlib.pyplot.ylabel(ylabel)
    if len(mode_names) > 1:
        matplotlib.pyplot.legend()
    matplotlib.pyplot.savefig(out_file)