I just upgraded to the App Engine 1.7.6 SDK for my python app and realised that breakpoints no longer work in PyDev (Eclipse plugin) when using the new dev_appserver.p
Yep, ran into the same problem.
Open your Run/Debug Configuration and set the Main Module to:
${GOOGLE_APP_ENGINE}/old_dev_appserver.py
Do you mean pdb.set_trace() isn't working?
Look for the function MonkeyPatchPdb() in google/appengine/tools/dev_appserver.py
Run that somewehere in your own project before you use pdb and it should fix it.
UPDATE 2012-07-27:
Following the comment, I verified, the issue is solved after updating to PyDev. 2.8 and App Engine 1.8.2
OBSOLETE:
I found the following analysis of the problem at googleappengine issues tracker
The reason why PDB doesn't work is because dev_appserver is using stdin/stdout for interprocess communication. Python has built-in libraries for IPC: http://docs.python.org/2/library/ipc.html. dev_appserver should use these, and then stdin/stdout can be left alone so that PDB still works.
So it seems that there is no workaround, rather than reverting to use old_dev_appserver.py
UPDATE 2013-04-23: Inability to debug is annoying. Many developers complain about it
I am keeping track of the development of this issue here: http://goo.gl/XRU01