[Python-Dev] Patch to use dict subclasses in eval(), exec

[Jeff Epler]

Still working from the version which is missing DECREFs, I get these
timings from a program intended to more directly measure the speed of
local, global, and builtin name lookups:

Vanilla Python CVS.  In effect these are three runs of the same thing,
so you get some idea of the timing variations on my system.
    $ python-cvs/python lookup-speed.py
    Timing 4000000 name lookups
        type  builtin   global    local overhead
        dict  2.74015  1.99215  1.21323  0.17610
           D  2.69901  1.99129  1.24662  0.17832
           E  2.73839  2.03171  1.25233  0.17843

CVS with my original patch (leaks references).  "D" is a dict subclass
which doesn't define __getitem__, "E" is a dict subclass which does
(simply calling dict.__getitem__ and returning the result)
    $ python-dict/python lookup-speed.py
    Timing 4000000 name lookups
        type  builtin   global    local overhead
        dict  2.81268  2.04795  1.26585  0.18117
           D  5.08308  2.85853  1.23625  0.17944
           E 81.62213 64.60481  1.26524  0.17973
This is a ~3% slowdown on the test with the heaviest use of builtins
and globals that I can think of offhand.  Slowdown:
            builtin global
     dict   3%      3%
        D   80%     40%
        E   *28     *31

I'm about done pretending to cheerlead for this patch, though if I fix
the reference problem I'll post the revised diffs.

Jeff