This is a followup to my mongodb-user post:
http://groups.google.com/group/mongodb-user/browse_thread/thread/18e3234c938de1c8
Please consider this patch for inclusion in the MongoDB Python driver.

Summary
-------
A patch that implements a bson.tzinfo module attribute that allows the
user to work with naive local datetimes which the driver automatically
converts to and from the recommended UTC storage format.

Use cases
---------
Web applications run on the server but are viewed and controlled from
the client browser:

• Clients and servers are are often in different timezones.
• Clients expect to view and input localized datetimes.
• Frameworks such as Django work best with naive local datetimes.
• Typically the client's timezone is available to the server in login
  profiles or possibly calculated using client-side JavaScript.

Non-Web apps are also simplified by not having to perform manual local
to UTC conversions.

How it works
------------
If the bson.tzinfo module attribute is set to a pytz timezone then:

• All naive datetimes feed to PyMongo are assumed to be in the
  bson.tzinfo timezone and are automatically converted UTC before
  being written to the database.

• All aware datetimes feed to PyMongo are automatically converted UTC
  before being written to the database.

• All (UTC) datetimes read from a database with PyMongo are
  automatically converted to aware datetimes in the bson.tzinfo
  timezone.

To set the timezone do something like this:

bson.tzinfo = pytz.timezone('Pacific/Auckland')

To revert to default PyMongo behavior:

bson.tzinfo = None

Most Linux distribution store the local Olson timezone name in
/etc/timezone – you can get a local tzinfo instance with something
like:

pytz.timezone(open('/etc/timezone').read().strip())

Implementation
--------------

• The attached patch is against PyMongo 1.9 (at Git commit b6b0e7d).
  Apply with:

patch -p1 <pymongo-timezone-transparency.patch

• The patch includes both Python and CPython implementations.
• The implementation is not dependent on pytz (but the user will need
  pytz to use the feature).
• I've also attached a simple standalone sanity checker test
  (timezone-transparency-test.py).