[Greg Ewing]
I think perhaps I'm not expressing myself very well. What I'm after is a high-level explanation that actually tells people something useful, and *doesn't* cop out by just saying "you're not experienced enough to understand this yet".
If such an explanation can't be found, I strongly suspect that this doesn't correspond to a cohesive enough concept to be made into a built-in language feature. If you can't give a short, understandable explanation of it, then it's probably a bad idea.
[Ping]
In general, i agree with the sentiment of this -- though it's also okay if there is a way to break the concept down into concepts that *are* simple enough to have short, understandable explanations.
I don't know. What exactly is the audience supposed to be of this high-level statement? It would be pretty darn impossible to explain even the for-statement to people who are new to programming, let alone generators. And yet explaining the block-statement *must* involve a reference to generators. I'm guessing most introductions to Python, even for experienced programmers, put generators off until the "advanced" section, because this is pretty wild if you're not used to a language that has something similar. (I wonder how you'd explain Python generators to an experienced Ruby programmer -- their mind has been manipulated to the point where they'd be unable to understand Python's yield no matter how hard they tried. :-) If I weren't limited to newbies (either to Python or to programming in general) but simply had to explain it to Python programmers pre-Python-2.5, I would probably start with a typical example of the try/finally idiom for acquiring and releasing a lock, then explain how for software engineering reasons you'd want to templatize that, and show the solution with a generator and block-statement. -- --Guido van Rossum (home page: http://www.python.org/~guido/)