code: def _get_column(self, column_or_label):
          
          c = column_or_label
          if isinstance(c, collections.Hashable) and c in self.labels:
              return self[c]
          elif isinstance(c, numbers.Integral):
              return self[c]
          elif isinstance(c, str):
              raise ValueError('label "{}" not in labels {}'.format(c, self.labels))
          else:
              assert len(c) == self.num_rows, 'column length mismatch'
              return c
docs: Convert label to column and check column length.