[XML-SIG] saxlib, xml, _xmlplus, etc.

[Martin v. Loewis]

Hi Mark,

Thanks for your elaboration of perl versioning mechanics. I agree that
the Python workings appear to be quite similar.

> with my limited python experience i haven't yet seen analogous
> abilities to declare an assumed python core version, or require a
> minimum version from another module.

Sure there is

import sys
assert sys.version_info > (2,0) # requires Python 2.0 or better

In fact, this is how the _xmlplus hack works. xml/__init__ has

_MINIMUM_XMLPLUS_VERSION = (0, 6, 1)
...
        v = _xmlplus.version_info
        if v >= _MINIMUM_XMLPLUS_VERSION:
            import sys
            sys.modules[__name__] = _xmlplus

This only installs "_xmlplus" as "xml" if _xmlplus is recent enough.
If you study that code, you'll notice that it also deals with the case
of old PyXML versions, which did not provide version_info.

> but i realize the purpose of this mailing list is not to educate me
> in python :).

It's ok, we are back to your original question.

Regards,
Martin