<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _ensure_tuple(item):
 """ Simply ensure that the passed item is a tuple. If it is not, then convert it if possible, or raise a NotImplementedError Args: item: the item that needs to become a tuple Returns: the item casted as a tuple Raises: NotImplementedError: if converting the given item to a tuple is not implemented. """

    if isinstance(item, tuple):
        return item
    elif isinstance(item, list):
        return tuple(item)
    elif isinstance(item, np.ndarray):
        return tuple(item.tolist())
    else:
        raise NotImplementedError