def tag_tranfsers(df):
    """Tag txns with description indicating tranfser payment."""
    df = df.copy()
    tfr_strings = [' ft', ' trf', 'xfer', 'transfer']
    exclude = ['fee', 'interest']
    mask = (df.transaction_description.str.contains('|'.join(tfr_strings))
            & ~df.transaction_description.str.contains('|'.join(exclude)))
    df.loc[mask, 'tag'] = 'transfers'
    return df