def tsg_count(driver_dataframe):
    """Function to count number of tumor suppressor genes from final driver gene dataframe."""
    tsg = driver_dataframe["driver_role"] == "TSG"
    df_tsg = driver_dataframe[tsg][["gene", "driver_role"]
                                   ].drop_duplicates().reset_index(drop=True)
    return len(df_tsg.index)