def listify(string_or_list):
    """
    return a list if the input is a string, if not: returns the input as it was

    Args:
        string_or_list (str or any):

    Returns:
        A list if the input is a string, if not: returns the input as it was

    Note:
        - allows user to use a string as an argument instead of single lists
        - cols='icd10' is allowed instead of cols=['icd10']
        - cols='icd10' is transformed to cols=['icd10'] by this function

    """
    if isinstance(string_or_list, str):
        string_or_list = [string_or_list]
    return string_or_list