[Python-3000] PEP for Metaclasses in Python 3000 (original) (raw)

Josiah Carlson jcarlson at uci.edu
Sat Mar 10 09:55:00 CET 2007

Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

Jack Diederich wrote: > I am a very big fan of ordered dicts in classes. One possibility is that > suites in classes always store their order in a special dict that keeps a > side list of key order. A final invisible class decorator around > every class would then toss out the order and leave only a regular dict. Is it really necessary to toss out the order at all? I'm skeptical that class dictionaries are either created or modified anywhere near often enough for there to be any noticeable performance penalty here.

I agree. Very few classes have significantly more than a few hundred assignments or accesses during class body execution. I don't think speed is going to matter enough for us to care.

[snip]

The tuple can be a constant of the code object, so the only overhead is one extra item added to the dict at class creation time, and none at all for subsequent access to the class dict. And you don't even need a special kind of dict.

Strawman:

class foo:
    if ...:
        a = 1
        b = 2
    else:
        b = 1
        a = 2
    c = 3

Which is first, a or b? What if ... is runtime-dependent?

Also, depending on the use, one may want to know the order in a 'move to end' fashion (if a is assigned to multiple times, it ends up in the ordering as if only the last assignment was done).

More information about the Python-3000 mailing list