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