code: def _col_type_set(self, col, df):
          
          type_set = set()
          if df[col].dtype == np.dtype(object):
              unindexed_col = list(df[col])
              for i in range(0, len(df[col])):
                  if unindexed_col[i] == np.nan:
                      continue
                  else:
                      type_set.add(type(unindexed_col[i]))
              return type_set
          else:
              type_set.add(df[col].dtype)
              return type_set
docs: Determines the set of types present in a DataFrame column.
  
          :param str col: A column name.
          :param pandas.DataFrame df: The dataset. Usually ``self._data``.
          :return: A set of Types.