From python-dev:

On Fri, Jan 29, 2010 at 15:04,  <exarkun@twistedmatrix.com> wrote:
> On 10:47 pm, tjreedy@udel.edu wrote:
>>
>> On 1/29/2010 4:19 PM, Collin Winter wrote:
>>>
>>> On Fri, Jan 29, 2010 at 7:22 AM, Nick Coghlan<ncoghlan@gmail.com> wrote:
>>
>>> Agreed. We originally switched Unladen Swallow to wordcode in our
>>> 2009Q1 release, and saw a performance improvement from this across the
>>> board. We switched back to bytecode for the JIT compiler to make
>>> upstream merger easier. The Unladen Swallow benchmark suite should
>>> provided a thorough assessment of the impact of the wordcode ->
>>> bytecode switch. This would be complementary to a JIT compiler, rather
>>> than a replacement for it.
>>>
>>> I would note that the switch will introduce incompatibilities with
>>> libraries like Twisted. IIRC, Twisted has a traceback prettifier that
>>> removes its trampoline functions from the traceback, parsing CPython's
>>> bytecode in the process. If running under CPython, it assumes that the
>>> bytecode is as it expects. We broke this in Unladen's wordcode switch.
>>> I think parsing bytecode is a bad idea, but any switch to wordcode
>>> should be advertised widely.
>>
>> Several years, there was serious consideration of switching to a
>> registerbased vm, which would have been even more of a change. Since I
>> learned 1.4, Guido has consistently insisted that the CPython vm is not part
>> of the language definition and, as far as I know, he has rejected any byte-
>> code hackery in the stdlib. While he is not one to, say, randomly permute
>> the codes just to frustrate such hacks, I believe he has always considered
>> vm details private and subject to change and any usage thereof 'at one's own
>> risk'.
>
> Language to such effect might be a useful addition to this page (amongst
> others, perhaps):
>
>  http://docs.python.org/library/dis.html
>
> which very clearly and helpfully lays out quite a number of APIs which can
> be used to get pretty deep into the bytecode.  If all of this is subject to
> be discarded at the first sign that doing so might be beneficial for some
> reason, don't keep it a secret that people need to join python-dev to learn.
>

Can you file a bug and assign it to me?

-Brett