Add ability to get Olson/POSIX name of a timezone

[aschatten]

I want to save a timezone name in the database, so maybe it would be nice to have an ability to get Olson or POSIX name of the timezone.
Example:

>>> from dateutil import tz
>>> tzla = tz.gettz('America/Los_Angeles')
>>> print tzla.name
America/Los_Angeles
>>> tzla = tz.gettz('America/Los Angeles')
>>> print tzla.name
America/Los_Angeles
>>> tzmet = tz.gettz('MET')
>>> print tzla.name
MET

Please let me know what you think? I can try to implement this.

[pganssle]

This seems reasonable. Feel free to make a pull request. One thing I'd be a bit worried about is cross-platform compatibility here. You can probably pull it from the filename, but on *nix systems, I'm getting:

    >>> from dateutil import tz
    >>> tzla = tz.gettz('America/Los_Angeles')
    >>> print(tzla._filename)
    '/usr/share/zoneinfo/America/Los_Angeles'
    >>> tzmet = tz.gettz('MET')
    >>> print(tzmet._filename)
    '/usr/share/zoneinfo/MET'

Whereas on Windows I'm getting:

    >>> from dateutil import tz
    >>> tzla = tz.gettz('America/Los_Angeles')
    >>> print(tzla._filename)
    'America/Los_Angeles'
    >>> tzmet = tz.gettz('MET')
    >>> print(tzmet._filename)
    'MET'

I'm guessing this is because on the *nix systems it's using the system zoneinfo file, and on Windows it's using the one provided by dateutil. If you decide not to make a PR, I can dig into this later.

[systemcatch]

Hey @pganssle I had a go at implementing this.

(dateutil) chris@ThinkPad:~/dateutil$ python
Python 3.8.3 (default, Jul  7 2020, 18:57:36) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from dateutil import tz
>>> nyc=tz.gettz("America/New_York")
>>> nyc
tzfile('/usr/share/zoneinfo/America/New_York')
>>> nyc.zone_name
'America/New_York'

It's currently exposed on tzfile, let me know if that's acceptable and I can make a full PR. Otherwise I'll dig into the codebase more to find another way of doing it.

[jorisvandenbossche]

@systemcatch I would be interested in this functionality. Do you still have your implementation lying around? (and want to make a PR?)

[systemcatch]

Hey @jorisvandenbossche I will take a look but I have a feeling that local branch may be gone.

[pganssle]

At this point it's probably easiest to wait for #1130 to be done, and/or use zoneinfo.Zoneinfo, which exposes this information.

[jorisvandenbossche]

@pganssle thanks for that pointer, looking forward to that change then. About using zoneinfo.Zoneinfo instead, certainly agree that one should prefer that if possible, but for context: my question was triggered by https://issues.apache.org/jira/browse/ARROW-5248, where we would like to support dateutil timezone objects in pyarrow (so if our users (or pandas users) are still using dateutil instead of zoneinfo).