[Python-Dev] Stdlib and timezones, again

[Christian Heimes]

Am 30.09.2012 20:18, schrieb Gregory P. Smith:
> We never hear anyone complain because the corrections are not for
> English or other "western" languages that the majority of us speak.  ;)
> 
> Regardless, I think including a version of the database on windows
> releases makes sense.  Update it on a best effort basis before each .x
> minor release.  The documentation can make it clear that it is a
> changing database how to use an updated version with your application.
> 
> One additional thing I'd like to see: Don't let the successful importing
> of a 'pytzdata' module be the only way to get an updated tz database.
>  Create an API for someone to supply one themselves at runtime that is
> cleaner than shoving something into sys.modules['pytzdata'].  And define
> in which order they'll be used:
> 
> priority:
>   1) api call supplying tz data to the process.
>   2) pytzdata module if it exists
>   3) tz data from the underlying operating system
>   4) error.

I like your basic approach but I'm suggesting a slightly different
approach. Before I explain my proposal I like to get a naming convention
straight.

integrated tz database
----------------------

A copy of the Olson database that is shipped with every version of
Python (not just Windows). The integrated database is updated with every
feature release of Python.


system tz database
------------------

That's an interface to the operating system's or platform's tz database.
We probably have to provide multiple backends for different OSes, Java etc.


update tz database
------------------

A PyPI package that contains a current version of the Olson database. A
new version of the update tz should be provided by the Python core
developer team every time a new Olson database is available. The
updatetz must never be distributed with the Python source code and shall
not be installed by a distributor.
Optionally we can include the code that creates an update tz package
from a Olson database.


By default Python tries to load the updatetz first, then systemtz (if
available) and finally the integratedtz. A user can query the status and
version of the databases, set and get the currently used database with
three functions. The used database can also be set with an environment
variable:

 datetime.gettzdatabase() -> "integrated" or "system" or "update"
 datetime.settzdatabase(name)
 datetime.listtzdatabases() ->
   {"integrated": "version",
    "system": "???"
    "update": "version", # only if an update tz db is installed
   }
 PYTHON_TZDB = "integrated" or "system" or "update"

With this setup users get the full benefit of system updates but can use
the integrated or update database if they don't like the operating
system's data.

Christian