$"""$Containers of objects"""

class Container:

$"""$A container that holds objects.

This is an abstract class. Only child classes should be instantiated.

$"""$

def add$($self$,$ item: object$)->$ None:

$"""$Add to this Container.

$"""$

raise NotImplementedError$("$Implemented in a subclass"$)$

def remove$($self$)->$ object:

$"""$Remove and return a single item from this Container.

$"""$

raise NotImplementedError$("$Implemented in a subclass"$)$