[Python-Dev] PYC Magic

[M.-A. Lemburg]

Tim Peters wrote:
> 
> [M.-A. Lemburg]
> > The reason is that I don't want to break the -U scheme.
> 
> But -U doesn't work anyway:
> 
> > (-U changes the semantics of the language in a pretty nasty
> > way ... nothing works anymore ;-).
> 
> The only things -U have bought us are a bizarre definition of "magic
> number", code complication, and complaints from people who see -U in the
> "python -h" blurb and want to know why everything breaks when they try it.
> It may be a hack you want to use for internal testing, but stuff that's been
> broken since the day it was introduced, and makes no progress towards
> working, doesn't belong in the general release.

Wait... the -U option was added in order to be able to see how well
the 8-bit string / Unicode integration works. It's a know fact that
the Python standard lib is not Unicode compatible yet and that's
exactly what the -U option allows you to test (in a very simple
way).

In the long run, Python's std lib should move into the direction 
of being Unicode compatible, so I don't really see the need for
removing -U altogether. To reduce the noise about Python failing
to run with the option set, it may be a good idea to remove the
mentioning from the -h blurb, though.
 
> > I know it's a hack, but until someone comes up with a better way to
> > add flags to store PYC compile options, we'll have to stick with
> > it.
> 
> But there is no need to store info about PYC compile options:  -U is its
> only use now, and -U has never worked.  Since it's worse than useless,
> better to throw it out, then dream up a rational way to store PYC compile
> options if and when (and only if and when) there's an actual need for such.

The -U option is currently the only application of such a flag.
We will definitely have a need for these options in the future
to make the runtime aware of certain assumptions which have been
made in the compiled byte code, e.g. byte code using special
opcodes, byte code compiled for a different Python virtual
machine (once we get pluggable Python compiler / VM combos),
byte code which was compiled using special literal 
interpretations (such as in the -U case or when compiling
the source code with a different source code encoding 
assumption).

I would be more than happy to get rid off the current PYC magic hack 
for -U and have it replaced with a better and extensible alternative,
e.g. a combination of PYC version number and marhsalled option 
dictionary.

-- 
Marc-Andre Lemburg
CEO eGenix.com Software GmbH
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