Due to two issues introduced in the 1.2.6 release of the Python SDK, we are releasing version 1.2.7 today. This is a bugfix-only release with just a few minor changes (no new features or functionality); all users of App Engine for Python should upgrade to the new version, available on our Downloads page.
The two issues were:
Both are now fixed in 1.2.7.
There is no corresponding release for the Java language version of App Engine (the Java SDK remains at 1.2.6).