Revert Your (Python) Code From Existing Instance of App Engine
WHAT A DAY!
I just delete hundreds lines of code because I want to revert my last commit (of 1 file, should not all project) by typing this :
git reset --hard HEAD^
then BOOMB! hundreds lines of code I typed in the last few hours just gone... HAHAHAH.
After few minutes PANIC! I got the solution, by download my latest code from latest pushed code on App Engine .
appcfg.py download_app -A <your_app_id> -V <your_app_version> <output-dir>