Newer versions of svn support the --show-item argument:
svn info --show-item revision
For the revision number of your local working copy, use:
svn info --show-item last-changed-revision
You can use os.system() to execute a command line like this:
svn info | grep "Revision" | awk '{print $2}'
I do that in my nightly build scripts.
Also on some platforms there is a svnversion command, but I think I had a reason not to use it. Ahh, right. You can’t get the revision number from a remote repository to compare it to the local one using svnversion.