| [mediator](mediator.py) | an object that knows how to connect other objects and act as a proxy |

| [memento](memento.py) | generate an opaque token that can be used to go back to a previous state |

| [mvc](mvc.py) | model<->view<->controller (non-strict relationships) |

| [observer](observer.py) | provide a callback for notification of events/changes to data |

| [pool](pool.py) | preinstantiate and maintain a group of instances of the same type |

| [prototype](prototype.py) | use a factory and clones of a prototype for new instances (if instantiation is expensive) |