def preprocessing_tolist(preprocess):
    """
    Transform preprocess into a list, if preprocess contains a dict, transform the dict into a list of dict.

    Parameters
    ----------
    preprocess : category_encoders, ColumnTransformer, list, dict, optional (default: None)
        The processing apply to the original data

    Returns
    -------
    List
        A list containing all preprocessing.
    """
    list_encoding = preprocess if isinstance(preprocess, list) else [preprocess]
    list_encoding = [[x] if isinstance(x, dict) else x for x in list_encoding]
    return list_encoding