[Python-Dev] Why is Bytecode the way it is?

[Skip Montanaro]

    >> Perhaps we take the CPU analogy too far. Or perhaps there is
    >> something deep I misunderstand.

    Martin> Most certainly. This stuff is *way*, *extremely* more difficult
    Martin> to write than it is to read. Just try and see for yourself. 

I wrote the rattlesnake VM (three-address model) ages ago (1.4 or 1.5?).  I
got it mostly to work, but never quite 100%.  There were a couple
instructions which were difficult to map into the register model for some
reason.  I suspect there may be more today, though moves to write a
reasonable bytecode verifier may improve that situation.  Even if I had
gotten it to work 100%, I would have been left with the problem of tracking
updates to the stack-based VM - an internal implementation detail don't
forget - until a cutover to the register-based VM could be made, and there'd
be no guarantees that would ever happen.  (Keeping the stackless source
sync'd with the main CPython source must be a challenging task for Christian
Tismer.)

I still have the source if anyone's interested, though so much water has
passed under the bridge now that it would only be useful as a rough guide.
Forget "patch -p 0 < ..."!

Skip