def n_values(obj, keys):
    """Extract multiple values from `obj`
    Parameters
    ----------
    obj : dict
        A grow or data "object"
    keys : list
        A list of valid key names
        Must have at least one element
    Returns
    -------
    tuple
        The values for each key in `args`
    Notes
    -----
    Always use tuple unpacking notation (commas); see examples
    Examples
    --------
    >>> x = {'one' : 1, 'two' : 2}
    >>> one, = n_values(x, ['one']) # include the comma even for a single key
    >>> one, two = n_values(x, ['one', 'two'])
    """
    assert isinstance(obj, dict), '`obj` must be type dict'
    assert isinstance(keys, list), '`keys` must be type list'
    return tuple(obj[k] for k in keys)