Use a version number of 0.0.0 instead of ???. The latter leads to

invalid filenames on Windows when building without specifying a
version number in the setup script.

See also
http://mail.python.org/pipermail/distutils-sig/2001-November/002656.html

Bugfix candidate.

Lib/distutils/dist.py

@@ -1012,7 +1012,7 @@ class DistributionMetadata:
         return self.name or "UNKNOWN"
 
     def get_version(self):
-        return self.version or "???"
+        return self.version or "0.0.0"
 
     def get_fullname (self):
         return "%s-%s" % (self.get_name(), self.get_version())