I've been running GoogleAppEngineLauncher for a couple days, without incident.
This morning I installed the gcloud package from Google.
The issue is that now, regardless of where I run my AppEngine project from (GoogleAppEngineLauncher or using dev_appserver.py) it immediately 500's and the log is:
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/runtime/wsgi.py", line 85, in LoadObject
obj = __import__(path)
File "/Users/roger/python/app.myapp/main.py", line 1, in <module>
ImportError: No module named webapp2
I ran into the same problem yesterday and although I could not find why it was happening, I did manage to fix the problem.
I assume you did something similar to me where I installed gcloud using: "pip install --user gcloud" and got a ton of libraries installed into my site-packages directory. (I am using Mac OS X 10.11) What I found is that although I do a pip uninstall gcloud, a bunch of libraries are left behind. To fix the problem I deleted the following libraries from my site-packages directory:
gcloud protobuf* google
dev_appserver.py now can find the webapp module.
Here is the complete list of everything it installed if you want to delete it:
gcloud gcloud-0.13.0.dist-info google googleapis_common_protos-1.1.0-py2.7-nspkg.pth googleapis_common_protos-1.1.0-py2.7.egg-info httplib2 httplib2-0.9.2-py2.7.egg-info oauth2client oauth2client-2.0.2-py2.7.egg-info protobuf-3.0.0b2.post2-py2.7-nspkg.pth protobuf-3.0.0b2.post2.dist-info pyasn1 pyasn1-0.1.9.dist-info pyasn1_modules pyasn1_modules-0.0.8.dist-info rsa rsa-3.4.2.dist-info
Now someone better than me, needs to explain why this happened.
Finally the best way I found to install gcloud is using the instruction here: https://cloud.google.com/appengine/docs/python/tools/using-libraries-python-27