[Distutils] Detecting if a package was installed with an "extra"

[Nathan R. Yergler]

I'm working on an improvement to my RDFa parser and because it will
rely on an external tool, I'm using an extra to require it to be
explicitly required.  Is there a way to tell at runtime if an egg (for
the code running) was installed with an extra.  For example, detecting
the difference between:

easy_install foo[bar]

and

easy_install foo

when in foo.py?

Thanks,

Nathan