I modified my Google App Engine app to work with Mako. To do this, I followed this answer including the comments:
Mako templates with Google App Engine
However, once you get to loading templates from files, you run into a big problem. By default, Mako's Template from mako/template.py wants to create a temporary file to store your compiled template. As far as I can tell, GAE doesn't allow you to create a temp file though. Has anyone run into this and figured out a work-around?