ignoring some placeholders in string formatting

[Michal Ludvig]

Hi all,

when I've got a string, say:

URL="http://xyz/blah?session=%(session)s&message=%(message)s"

is it possible to fill in only 'session' and leave "%(message)s" as is
when it isn't present in the values dict?

For example:
URL % { 'session' : 123 }
raises KeyError because of missing 'message' in the dict.

I could indeed replace '%(session)s' with a string replace or regexp but
that's not very elegant ;-)

Is there any way to tell the formatter to use only what's available and
ignore the rest?

Thanks

Michal