On Sun, Apr 14, 2013 at 03:28:31PM +0100, Steven Hiscocks wrote: > On 14/04/13 03:36, David Strauss wrote: > >I keep writing lengthy emails about how we can use this as an > >opportunity to reduce redundancy and improve consistency, but I should > >probably ping you on #systemd IRC to hash it out. I can't think of > >anything elegant that doesn't involve altering the existing journal.py > >or _reader.c code. Hi Steven, hi David,
I read your discussion on IRC... I agree that backwards compatibility is not (yet) something that we need to keep very. I think that the number of people using those Python interfaces is quite small so far, and having a nice interface is more important than some small breakage. > >As a starter, I want to enumerate the places where > >__REALTIME_TIMESTAMP has special handling: > > (1) Existing code: A C-based member function in _reader.c. > > (2) Existing code: A native Python conversion function in journal.py. > > (3) Existing code: An entry in DEFAULT_CONVERTERS. > > (4) Added in your patch: A key setting in get_next(). > > (5) Added in your patch: A Python-based member function in journal.py > >that overrides (1). > > (6) Added in your patch: A condition in get() that invokes (1) when > >the specific field is requested. > > > >While I want to fix this bug, I also don't want six scattered special > >cases for __REALTIME_TIMESTAMP and similar fields. > > > > Thanks for the chat earlier on IRC David, especially given your > localtime :-). > > I thought about the points discussed: keeping things similar to > journalctl -o json output (i.e. include special fields); get, > get_next, and get_realtime, etc methods create duplication and > multiple ways to get the same/some values (could cause confusion); > issue with `next` clashing with python2 __iter__ next; trying to > stabilise the interface (note: not declared stable yet); performance > issues with unnecessary dictionary field conversions. > > I've therefore created another patch for consideration: > https://gist.github.com/kwirk/5382783 This looks pretty nice, and I think it can be committed. Could you create a patch with a commit message, including some of the rationale, so that people understand what's happenning? ;) > I've removed the get_next and get_previous methods from _Reader, as > these didn't align with the C API. This is replaced with:`_get_all` > private method (effectively a wrapper around C API macro > sd_journal_{enumerate,restart}_data/SD_JOURNAL_FOREACH_DATA); > renamed `next` method to `_next`, such to avoid name clash (and I > believe should be private); `_previous` method for consistency. > > The `get_next` and `get_previous` methods are now in Reader only. > These call `_next` method, followed by `_get_all` and then fetch the > special fields, before passing whole dictionary to converters. This > makes all the traversal, and getting standard and special fields > from the journal transparent to the user. > > With the changes of removing `get_next` in _Reader, the iter methods > don't function as you'd expect. To that end, I've moved them to > Reader with get_next as iter next call as before. > > I understand the points about performance, but don't think the > performance hit is that bad, or critical in most use cases. These > changes should allow a custom class to inherit _Reader, and the > create a more optimised version if that is required. (One option if > this is a major issue, is a custom dictionary class could be > returned by `get_next`, which uses the __get__ method to lazy > convert the fields on access. This is starting to get complicated > thought...) I think we can always do that later on. Maybe it makes sense to document that get_next() returns something dictionary-like (collections.abc.Mapping) that right now is just a dict, but could become something different later on. Zbyszek _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
