def out_of_date(original, derived):
    return (not os.path.exists(derived) or
            (os.path.exists(original) and
             os.stat(derived).st_mtime < os.stat(original).st_mtime))
Returns True if derivative is out-of-date wrt original,
dataset/ETHPy150Open mwaskom/seaborn/doc/sphinxext/plot_directive.py/out_of_date