docs: def get_column(self, position, missing_seqs=MissingSequenceHandler.SKIP):
      """
      return a column from an alignment as a dictionary indexed by seq. name.
  
      :param position:     the index to extract; these are in alignment
                           co-ordinates, which are one-based, so the first column
                           has index 1, and the final column has
                           index == size(self).
      :param missing_seqs: how to treat sequence with no actual sequence data for
                           the column.
      :return: dictionary where keys are sequence names and values are
               nucleotides (raw strings).
      """
      res = {}
      for k in self.sequences:
        if isinstance(self.sequences[k], UnknownSequence):
          if missing_seqs is MissingSequenceHandler.TREAT_AS_ALL_GAPS:
            res[k] = "-"
          elif missing_seqs is MissingSequenceHandler.SKIP:
            continue
        else:
          res[k] = self.sequences[k][position - 1]
      return res