def get_msg(feat, mpnn, train_folder):
    """
    Create a message telling the user what kind of model we're training.
    Args:
      feat (bool): whether this model is being trained with external features
      mpnn (bool): whether this model is being trained with an mpnn (vs. just with
        external features)
      train_folder (str): path to the training folder
    Returns:
      msg (str): the message
    """

    msg = "Training a ChemProp model with "
    if feat:
        msg += "set features "
    if feat and mpnn:
        msg += "and "
    if mpnn:
        msg += "an MPNN "

    msg += f"in folder {train_folder}\n"

    return msg