I submitted my proposal for PyOhio 2009

Here it is: Clever uses for metaclasses


This talk introduces metaclasses and attempts to “defang” them, showing what they are good for, and when they are silly.

Metaclasses can reduce redundancy in code but can be very confusing, so in this talk, I will walk through several examples of how to use metaclasses to solve problems.

I plan to cover (at least) these examples:

  • Add extra methods and attributes to a class after its definition.
  • Verify a class correctly implements a specification.
  • Give a subclass its own class-variables rather than sharing them with the parent class.
  • Implement the basics of an object-relational mapper (ORM).

I published an article in the November 2008 issue of Python Magazine with the same title (Clever Uses for Metaclasses) and I’ll use some code from that article.

I want to give this talk in a friendly, informal manner, so that people that feel intimidated by metaclasses realize that there’s nothing to be scared of.


This talk is aimed at the intermediate-level programmer, already familiar with object-oriented concepts and is really comfortable with Python.

I do not expect people in the audience to know ANYTHING about metaclasses before this talk.


  • object-oriented programming
  • metaprogramming
  • dynamic language tomfoolery
  • introspection

3 thoughts on “I submitted my proposal for PyOhio 2009

  1. Matt,

    Hey did you think of using class decorators instead of metaclasses? I think you can do all that with class decorations, and probably easier to understand.

  2. Yeah, I agree about class decorators being a good substitute. The big
    difference with class decorators is that they don't apply to
    subclasses, so you have to keep applying them in each subclass.

    For maximum confusion, maybe metaclasses could apply class decorators,
    and class decorators might be made to depend on code built by the

    I like writing articles and exploring these wacky corners, but when it
    comes to write, I try to keep my stuff as stupid as possible. All the
    dynamic tomfoolery is awesome when it works, but it is hellish to


  3. Meta classes really confuses me too. Ya. I have read the Clever Uses for Metaclasses. It is very nice. Nice explanations are given. Thanks for sharing.
    by thoi trang

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