Debug Jinja2 in Google App Engine

Question

When I\'m running Jinja2 in Google App Engine, I get useless debugging information. I gather this is because of this item in the FAQ:

My tracebacks l

Answer 1

You can get around this by adding _ctypes and gestalt to the development server's C module whitelist with monkeypatching.

To do so, put the following snippet at the top of your main.py:

import os
if os.environ.get('SERVER_SOFTWARE', '').startswith('Dev'):
    # Enable ctypes for Jinja debugging
    from google.appengine.tools.dev_appserver import HardenedModulesHook
    HardenedModulesHook._WHITE_LIST_C_MODULES += ['_ctypes', 'gestalt']

You can also use this trick to enable other C modules, if you have similar local-only module needs. Do note that these modules still won't actually work once you deploy, so tread carefully.

On SDK 1.6.3 using python2.7 you need to change the above code to:

import os
if os.environ.get('SERVER_SOFTWARE', '').startswith('Dev'):
    # Enable ctypes for Jinja debugging
    import sys
    from google.appengine.tools.dev_appserver import HardenedModulesHook
    assert isinstance(sys.meta_path[0], HardenedModulesHook)
    sys.meta_path[0]._white_list_c_modules += ['_ctypes', 'gestalt']

On SDK 1.8.6 for python 2.7, try this:

PRODUCTION_MODE = not os.environ.get(
    'SERVER_SOFTWARE', 'Development').startswith('Development')
if not PRODUCTION_MODE:
    from google.appengine.tools.devappserver2.python import sandbox
    sandbox._WHITE_LIST_C_MODULES += ['_ctypes', 'gestalt']