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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 run_ffitch(distfile, outtreefile, intreefile=None, **kwargs):
 """ Infer tree branch lengths using ffitch in EMBOSS PHYLIP """

    cl = FfitchCommandline(datafile=distfile, outtreefile=outtreefile, \
            intreefile=intreefile, **kwargs)
    r, e = cl.run()

    if e:
        print("***ffitch could not run", file=sys.stderr)
        return None
    else:
        print("ffitch:", cl, file=sys.stderr)
        return outtreefile