Use GaussSum to automatically generate UV-Vis spectra

uvvis.py

"""Script to plot UV-Vis spectrum using GaussSum

Before running, set the PYTHONPATH to the directory containing GaussSum.py.
This script runs the UV-Vis spectrum generator across every .out file
in the current folder.
"""

import os
import sys
import glob
import logging

from gausssum.electrontrans import ET
from gausssum.cclib.parser import ccopen

ver = "2.2"
def gaussdir(filename):
    return os.path.join(os.path.dirname(filename), "gausssum%s" % ver)

if __name__ == "__main__":
    start, end = 200, 500
    numpts, fwhm = 500, 3000

    filenames = glob.glob("*.out")
    for filename in filenames:
        log = ccopen(filename)
        log.logger.setLevel(logging.ERROR)
        data = log.parse(filename)

        ET(None, sys.stdout, data, filename, start, end, numpts, fwhm, True,
           None, False)
        os.rename(gaussdir(filename), filename.split(".")[0] +"_gs")

I am trying your script, and as I am not very used to python yet, so I am getting this error:

/usr/local/lib/python3.6/site-packages/matplotlib/__init__.py:1401: UserWarning:  This call to matplotlib.use() has no effect
because the backend has already been chosen;
matplotlib.use() must be called *before* pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.
warnings.warn(_use_error_msg)

Could you help me, please?
Thank you in advance