def is_model_instance(engine):
    """
    Determines if `engine` is an instance of an izzy model instance.

    Parameters
    ----------
    engine : object
        An izzy model instance.

    Returns
    -------
    bool
        True or False if engine is an izzy instance.
    """
    return isinstance(engine, object) & (getattr(engine, '_package', None) ==
        'izzy')
