[systemd-devel] python - reading the journal

[Zbigniew Jędrzejewski-Szmek]

On Thu, Feb 21, 2013 at 06:46:35PM +0000, Steven Hiscocks wrote:
> On 21/02/13 01:49, Zbigniew Jędrzejewski-Szmek wrote:
> >On Tue, Feb 19, 2013 at 09:02:56PM +0000, Steven Hiscocks wrote:
> >>I've pushed a few more commits.
> >I've pushed a few commits to
> >https://github.com/keszybz/systemd/commits/python-systemd-reader
> >This is your tree but rebased onto my id128 stuff, and modified
> >to use it. It also has sphinx-generated documentation and gcc
> >all warnings fixed. Please have a look.
> >
> >Zbyszek
> >
> 
> Thanks Zbyszek. Looks really good. Tidied it up a bit :)
> 
> With the macros for python 2 and 3 differences:
> I wonder if unicode_FromString is a bit confusing, as the macro
> returns a string and not Unicode for python2? Same for long_AsLong,
> which returns int in python2?
I don't think that this matters too much. There's a comment about
the naming convention before the macros, and anyway this is purely
internal stuff.

> Also, not related to the commits:
> I've noted that `sd_journal_get_cursor` man pages states that it
> returns 0 on success, but it actually returns 1. Note sure if the
> code or man page is in error. There is a comment in _reader.c
> get_next against `sd_journal_get_cursor`, which I guess needs to be
> removed once this is clarified.
This has been now fixed in the master branch.

I've pushed a few more commits to 
https://github.com/keszybz/systemd/commits/python-systemd-reader.
Important changes:

1. Checks for return values of all function calls, so now
everything should fail nicely, even on OOM conditions. This
lengthens the code quite a bit, but seems unavoidable.

2. The value returned for __TIMESTAMP_MONOTONIC:
both fields are returned as a tuple. Under Python 3
a named tuple is used:

>>> from systemd import journal
>>> t = journal.Journal().get_next()
>>> t['__MONOTONIC_TIMESTAMP'].timestamp
datetime.timedelta(0, 15, 368483)
>>> t['__MONOTONIC_TIMESTAMP'].bootid
UUID('9838676e-2666-4a83-b8be-b0654747f8be')

I think that this is relatively lightweight, yet nice to use.

Under Python 2.7, a normal tuple is returned, so it is necessary
to use t['__MONOTONIC_TIMESTAMP'][0], t['__MONOTONIC_TIMESTAMP'][1].

I first tried with a class, and it felt too complicated.

3. Sphinx documentation can be generated with 'make destdir-sphinx'.
This target is part of 'make doc-sync', which means that the documents
will be uploaded along with the man pages to freedesktop.org.
So when this is merged
  http://www.freedesktop.org/software/systemd/man/python-systemd
will be the URL with docs. Preview is at:
  http://keszybz.github.com/systemd/python-systemd/

This way that the docs are generated is not very nice (whole package
is installed using random DESTDIR, and sphinx-build is run with
PYTHONPATH and LD_LIBRARY_PATH pointing to this directory), but seems
to work. The documentation is only generated on request, i.e. only by
conscious developers, so it's not catastrophic even if this doesn't
always work.

I think that this is becoming mergeable.

Zbyszek