def append(nodelist, node, label=None, sep='_'):
    """
    Append function to automate the naming of list elements in Containers.

    :Arguments:
        - `nodelist` : List containing nodes for Container.
        - `node` : Node to be added to list.
        - `label` : Label to be appended to list (If not passed,
        defaults to element number).
        - `sep` : Separator character for label (defaults to underscore).

    :Return:
        - `nodelist` : Passed list with node added.

    """
    nname = node.__name__
    label = label or len(nodelist)
    ind = nname.rfind(sep)
    node.__name__ = nname[:ind] + sep + str(label)
    nodelist.append(node)
    return nodelist
