Basically (I don't understand this satisfactorily either) : represent meta concepts of the object system inside the object system itself. As always, the best w

Basically (I don't understand this satisfactorily either) : represent meta concepts of the object system inside the object system itself. As always, the best way to make sense of it is with an example. One example is meta classes in python. Classes, those 'blueprints' that we create objects in their image? they are themselves but objects, their class is called 'type', it's a special kind class, a meta class (a class whose objects are themselves classes). You can inherit this type and create your own meta class, and that lets you do various cool things. For one thing, object creation in python is done by calling the object' s class as if it's a function. Now this is a method call (__call__), where do methods reside? in the class off course. So for classes, the __call__ reside in the meta class. When python says you can inherit this class, you listen very carefully. This means you can inject arbitary code during the instance creation process. Now every class that is an instance of your meta class can email you whenever somebody wants to create an object from it. It's like the interpreter is giving you a hook to something incredibly intimate and private to the VM, exposing it from within the interpreted language itself (and not as a C API for example) meta classes is a kind of MOP for python because it represents intimate details about an object system ('hey, what exactly happens when we ask a class for an object?') inside that object system itself ('it calls this particular method, which you are more than welcome to override and augment as you please without leaving the comfort of the language').