MVC in software engineering
The model stores data, and runs domain-specific logic. An example of domain-specific logic in the banking domain is
if customer's account is below zero, refuse withdrawals.
The view gets data to display from the model. Some MVC have the view pull data from the model itself, others have the view notified by the model, and others have the controller tell the view to update itself.
The controller receives and converts user inputs in actions understandable by the model. In web development, such as ASP.net or Java servlets, the controller picks which view is going to be displayed, and then the selected view is actually in charge of displaying information on the screen.
If this description is not clear enough, the wikipedia page about MVC has a scenario that helps explain how the model, view and controller fit together.
MVC in games
Many amateur game developers say
ideas from MVC can be applied to games but in general it is just a waste of time. For many, there is no such thing as game architecture:
The only difference with classic MVC is that in a game, the graphics data, logic and game algorithm is fused together. Others argue that in a rapid prototyping context, where iterating is key, one should not waste time conceiving a modular/maintainable system, but rather focus on testing the game as fast as possible.
Many non-indie games are made with MVC in mind. Splitting data from presentation induces extra work on the code and managing slightly more objects in memory. However, this is exactly what allows an easier testing and debugging of mechanics, UI, and network components. In fact, MVC has been applied to game programming since at least 1998. A blogger at TigSource states that MVC can be applied in any part of a game. Taking the example of a network connection:
The input view in this case is a network receiver running in it's own thread and listening for data from a socket. When the view receives data, it's translated into an internal class and sent to a controller for processing.
I find that explicitly implementing an MVC pattern for the network connection is a bit of an exaggeration. Heads-up displays and other UI input perfectly fit as controllers, and are naturally decoupled from the model. On the other hand, there is a strong tendency by many game developers to ignore software engineering practices. Some even put forward the Extreme Programming side of rapid prototyping to justify their ignorance of any architecture. Agile methods do not contradict the use of any architectural pattern.
That may explain why so many of pygame's projects contain a single file with thousands of lines of code ...