def cat_imputer(trfm, col_names):
    """

    Parameters
    ----------
    trfm :
        Contains the Sklearn's Imputer preprocessing instance
    col_names : list
        Contains list of feature/column names.
        The column names may represent the names of preprocessed attributes.

    Returns
    -------
    pp_dict : dictionary
        Returns a dictionary that contains attributes related to Imputer preprocessing.

    """
    derived_colnames = col_names
    pp_dict = dict()
    derived_flds = list()

    mining_strategy = "asMode"
    mining_replacement_val = trfm.fill_

    pp_dict['mining_strategy'] = mining_strategy
    pp_dict['mining_replacement_val'] = mining_replacement_val
    pp_dict['mining_attributes'] = col_names
    pp_dict['der_fld'] = derived_flds
    pp_dict['der_col_names'] = derived_colnames

    return pp_dict