Make generated Python code importable

[moraes]

Currently the compiled Python code generated by Jinja2 is not importable because it uses a 'environment' variable injected during exec. Wrapping the generated code by a function would make it usable through import, creating a new modality of template loading - import as module.

It's an edge case, but it's super fast and would be particularly useful in App Engine - where we need to use precompiled templates to have a performance comparable to the one provided by the bytecode cache.

The idea: since we are precompiling templates on deployment, why go through compile() and exec while we can simply import the precompiled code as a module and run it? Making the generated code importable would allow this, while keeping other loading methods unaffected.

A proof of concept is here:

http://paste.pocoo.org/show/124381/

And the related discussion is here:

http://groups.google.com/group/pocoo-libs/browse_thread/thread/748b0d2024f88f64?pli=1

[moraes]

Obs: jinja2.debug is the only part uncovered by the proof of concept, afaik.

I tried to fit it, but had a hard time trying to understand what is happening there. :-P

[moraes]

Obs2: this started with this tool I created to precompile template directories to use in App Engine:

http://bitbucket.org/moraes/appengine/src/tip/gaefy/jinja2/compiler.py

The saved code is then loaded using a special loader:

http://bitbucket.org/moraes/appengine/src/tip/gaefy/jinja2/code_loaders.py

While it greatly improves performance in App Engine, it is still much slower than using bytecode cache. Importing the templates as modules would be as fast or faster than using bytecode cache.

[moraes]

Here's a cleaner version, without touching the __jinja_template__ variable passed in the namespace, and so not modifying globals in the compiled code:

http://paste.pocoo.org/show/131061/

[moraes]

Calling the function template() is probably a bad choice, but you get the idea... :-) Here it is back to run(), anyway:

http://paste.pocoo.org/show/131062/

[moraes]

Some more info for testing. To compile templates as modules:

http://bitbucket.org/moraes/appengine/src/tip/gaefy/jinja2/compiler.py

To load templates as modules:

http://bitbucket.org/moraes/appengine/src/tip/gaefy/jinja2/module_loaders.py