code: def _to_seq(sc, cols, converter=None):
      
      if converter:
          cols = [converter(c) for c in cols]
      return sc._jvm.PythonUtils.toSeq(cols)
docs: Convert a list of Column (or names) into a JVM Seq of Column.
  
      An optional `converter` could be used to convert items in `cols`
      into JVM Column objects.