def oncogenes_count(driver_dataframe):
    """Function to count number of oncogenes from final driver gene dataframe."""
    oncogene = driver_dataframe["driver_role"] == "Oncogene"
    df_oncogene = driver_dataframe[oncogene][[
        "gene", "driver_role"]].drop_duplicates().reset_index(drop=True)
    return len(df_oncogene.index)