Extract index and watch from :class:`Blocking`

    Parameters:
        obj (Blocking): the blocking object
    Returns:
        tuple: index and watch

def extract_blocking(obj):
    """Extract index and watch from :class:`Blocking`

    Parameters:
        obj (Blocking): the blocking object
    Returns:
        tuple: index and watch
    """
    if isinstance(obj, tuple):
        try:
            a, b = obj
        except:
            raise TypeError("Not a Blocking object")
    else:
        a, b = obj, None
    return extract_attr(a, keys=["Index"]), b