Prefer to put arguments on one line if they fit.

Something like this:

 raise MultiProjectException(
     "Ambiguous workspace: %s=%s, %s" %
     (varname, varname_path, os.path.abspath(config_filename)))

instead of this:

 raise MultiProjectException(
     "Ambiguous workspace: %s=%s, %s" % (
         varname,
         varname_path,
         os.path.abspath(config_filename)))