[XML-SIG] Finding _xmlplus in Python 2.3a2

[Brian Quinlan]

> The same is true for any other software package. Any change in a
> package can cause applications to stop working. So if you don't want
> to risk a breakage, don't upgrade any software.

> I cannot see how this is relevant to the _xmlplus technique, though.

A script author can't necessarily control the runtime environment of
their software. If I have a script beginning with:

#!/usr/bin/env python2.1

import string

I can be reasonably sure that the string library that I am getting is
the one that I have tested with (perhaps with some bug fixes). This is
not the case if I import from the xml package.

This actually caused some confusion when I worked at ActiveState: every
developer had the same version of ActivePython installed but some Web
Services code would exhibit different behavior on different machines.
Eventually the problem was tracked done to some developers having PyXML
installed. 

> The same is true for any other setup. If you upgrade the system's C
> library, you don't expect Apache to stop working, if you don't know
> the details of the setup. If you upgrade Perl, you don't expect
> spamassassin to stop working, if you don't know the details of the
> setup.

I think that popular C libraries tend to achieve a higher level of
compatibility than Python's XML libraries do.

Cheers,
Brian