def get_conversion_rate(df, total, conversions):
    """Return the conversion rate of column.

    Args:
        :param df: Pandas DataFrame.
        :param total: Column containing the total value.
        :param conversions: Column containing the conversions value.

    Returns:
        Conversion rate of conversions / total

    Example:
        df['cr'] = get_conversion_rate(df, 'sessions', 'orders')

    """

    value = (df[conversions] / df[total])
    return value