def to_lowercase(df, column_names=[]):
    """
    This function transforms strings of the column names in the dataframe
    passed to lowercase

    Args:
        df (pd.DataFrame): Raw dataframe with some text columns.
        column_names(list, optional): column names to be changed to lowercase.

    Returns:
        pd.DataFrame: Dataframe with columns with lowercase standardization.
    """
    if not column_names:
        return to_lowercase_all(df)
    else:
        df[column_names] = df[column_names].applymap(lambda s: s.lower() if type(s) == str else s)
        return df

    This function transforms strings of the column names in the dataframe
    passed to lowercase

    Args:
        df (pd.DataFrame): Raw dataframe with some text columns.
        column_names(list, optional): column names to be changed to lowercase.

    Returns:
        pd.DataFrame: Dataframe with columns with lowercase standardization.
    
utils_nlp/dataset/preprocess.py