[Zope3-dev] More pytz pickling; 'zone' attribute

[Gary Poster]

Hi Stuart.  Hope all is well.

When last we spoke, we got the UTC timezone to be picklable.  I'd  
like to let pytz timezones pickle also (so we can persist a user's  
preferred timezone).  While I could keep the timezone name around,  
I'd prefer to keep the timezone object itself.

Adding a reduce to tzinfo.py's BaseTZInfo, a la

class BaseTzInfo(tzinfo):
     # Overridden in subclass
     _utcoffset = None
     _tzname = None
     zone = None

     def __str__(self):
         return self.zone

     def __reduce__(self):
         return self.__class__.__name__

accomplishes this for all of the included timezones.  It would break  
if someone tried to use the __init__ arguments in DstTzInfo, but grep  
tells me that nothing is doing that right now in the package.

Therefore, I propose the following:

- add a __reduce__ as shown above

- eliminate the __init__ arguments in DstTzInfo since they are not  
used and would break pickling if they were

- document and test the contract that the timezones may be pickled,  
and that loading the pickle returns the same original instance (i.e.,  
it's a singleton)

On a somewhat unrelated note, I noticed that dst() and tzname() were  
not implemented per the standard library's spec; upon reflection, I  
decided that this might be because the Olson database made this  
difficult or impossible.  Feel free to clarify or not; the point is  
that I would like to use a name for the timezone, and the 'zone'  
attribute seems to do enough what I want, even though it is not  
daylight-savings aware.

Therefore I further propose that the zone attribute be exposed in  
docs as a reliable attribute of the pytz timezones, and the key  
through which it is accessible from pytz.timezone.

If that is a contract, BaseTZInfo's __reduce__ could instead

     return pytz.timezone, (self.zone)

, which might be more forward compatible (and not require DstTzInfo's  
__init__ signature to change).

Thoughts?

Thanks

Gary