def fillna(df, method="zeros"):
    """
    Fill empty values in a Data Frame with the chosen method.
    Valid options for method are: zeros, mean, median, mode
    """

    if method == "mean":
        return df.fillna(df.mean())
    elif method == "median":
        return df.fillna(df.median())
    elif method == "mode":
        return df.fillna(df.mode().iloc[0])
    elif method == "none":
        return df
    else:
        return df.fillna(0)