Archiv für Januar 2011

Na zdraví PyGI!

(Update: Link to Tomeu’s blog post, repost for planet.gnome.org)

Last week I was in Prague to attend the GNOME/Python 2011 Hackfest for gobject-introspection, to which Tomeu Vizoso kindly invited me after I started working with PyGI some months ago. It happened at a place called brmlab which was quite the right environment for a bunch of 9 hackers: Some comfy couches and chairs, soldering irons, lots of old TV tubes, chips, and other electronics, a big Pirate flag, really good Wifi, plenty of Club Mate and Coke supplies, and not putting unnecessary effort into mundane things like wallpapers.

It was really nice to get to know the upstream experts John (J5) Palmieri and Tomeu Vizoso (check out Tomeu’s blog post for his summary and some really nice photos). When sitting together in a room, fully focussing on this area for a full week, it’s so much easier to just ask them about something and getting things done and into upstream than on IRC or bugzilla, where you don’t know each other personally. I certainly learned a lot this week (and not only how great Czech beer tastes :-) )!

So what did I do?

Application porting

After already having ported four Ubuntu PyGTK applications to GI before (apport, jockey, aptdaemon, and language-selector),
my main goal and occupation during this week was to start porting a bigger PyGTK application. I picked system-config-printer, as it’s two magnitudes bigger than the previous projects, exercises quite a lot more of the GTK GI bindings, and thus also exposes a lot more GTK annotation and pygobject bugs. This resulted in a new pygi s-c-p branch which has the first 100 rounds of “test, break, fix” iterations. It now at least starts, and you can do a number of things with it, but a lot of functionality is still broken.

As a kind of “finger exercise” and also to check for how well pygi-convert works for small projects now, I also ported computer-janitor. This went really well (I had it working after about 30 minutes), and also led me to finally fixing the unicode vs. str mess for GtkTreeView that you got so far with Python 2.x.

pygobject and GTK fixes

Porting system-config-printer and computer-janitor uncovered a lot of opportunities to improve pygi-convert.sh, a big “perl -e” kind of script to do the mechanical grunt work of the porting process. It doesn’t fix up changed signatures (such as adding missing arguments which were default arguments in PyGTK, or the ubiquitous “user_data” argument for signal handlers), but at least it gets a lot of namespaces, method, and constant names right.

I also fixed three annotation fixes in GTK+. We also collaboratively reviewed and tested Pavel’s annotation branch which helped to fix tons of problems, especially after Steve Frécinaux’s excellent reference leak fix, so if you play around with current pygobject git head, you really also have to use the current GTK+ git head.

Speaking of which, if you want to port applications and always stay on top of the pygobject/GTK development without having to clutter your package system with “make install”s of those, it works very well to have this in your ~/.bashrc:

export GI_TYPELIB_PATH=$HOME/projects/gtk/gtk:$HOME/projects/gtk/gdk
export PYTHONPATH=$HOME/projects/pygobject

Better GVariant/GDBus support

The GNOME world is moving from the old dbus-glib python bindings to GDBus, which is integrated into GLib. However, dbus-python exposed a really nice and convenient way of doing D-Bus calls, while using GDBus from Python was hideously complicated, especially for nontrivial arguments with empty or nested arrays:

from gi.repository import Gio, GLib
from gi._gi import variant_type_from_string

d = Gio.bus_get_sync(Gio.BusType.SESSION, None)
notify = Gio.DBusProxy.new_sync(d, 0, None, 'org.freedesktop.Notifications',
    '/org/freedesktop/Notifications', 'org.freedesktop.Notifications', None)

vb = GLib.VariantBuilder()
vb.init(variant_type_from_string('r'))
vb.add_value(GLib.Variant('s', 'test'))
vb.add_value(GLib.Variant('u', 1))
vb.add_value(GLib.Variant('s', 'gtk-ok'))
vb.add_value(GLib.Variant('s', 'Hello World!'))
vb.add_value(GLib.Variant('s', 'Subtext'))
# add an empty array
eavb = GLib.VariantBuilder()
eavb.init(variant_type_from_string('as'))
vb.add_value(eavb.end())
# add an empty dict
eavb = GLib.VariantBuilder()
eavb.init(variant_type_from_string('a{sv}'))
vb.add_value(eavb.end())
vb.add_value(GLib.Variant('i', 10000))
args = vb.end()

result = notify.call_sync('Notify', args, 0, -1, None)
id = result.get_child_value(0).get_uint32()
print id

So I went to making the GLib.Variant constructor work properly with nested types and boxed variants, adding Pythonic GVariant iterators and indexing (so that you can treat GVariant dictionaries/arrays/tuples just like their Python equivalents), and finally a Variant.unpack() method for converting the return value of a D-Bus call back into a native Python data type. This looks a lot friendlier now:

from gi.repository import Gio, GLib

d = Gio.bus_get_sync(Gio.BusType.SESSION, None)
notify = Gio.DBusProxy.new_sync(d, 0, None, 'org.freedesktop.Notifications',
    '/org/freedesktop/Notifications', 'org.freedesktop.Notifications', None)

args = GLib.Variant('(susssasa{sv}i)', ('test', 1, 'gtk-ok', 'Hello World!',
    'Subtext', [], {}, 10000))
result = notify.call_sync('Notify', args, 0, -1, None)
id = result.unpack()[0]
print id

I also prepared another patch in GNOME#640181 which will provide the icing on the cake, i. e. handle the variant building/unpacking transparently and make the explicit call_sync() unnecessary:

from gi.repository import Gio, GLib

d = Gio.bus_get_sync(Gio.BusType.SESSION, None)
notify = Gio.DBusProxy.new_sync(d, 0, None, 'org.freedesktop.Notifications',
    '/org/freedesktop/Notifications', 'org.freedesktop.Notifications', None)

result = notify.Notify('(susssasa{sv}i)', 'test', 1, 'gtk-ok', 'Hello World!',
            'Subtext', [], {}, 10000)
print result[0]

I hope that I can get this reviewed and land this soon.

Thanks to our sponsors!

Many thanks to the GNOME Foundation and Collabora for sponsoring this event!

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New tool to check support status of dependencies

A common source of unnoticed depwaits or uninstallability are main packages which introduce new build or binary dependencies from universe. These either require fixing, or filing a main inclusion report.

To help with this, I added a new check-mir script into ubuntu-dev-tools version 0.110, which walks through all build and binary dependencies, checks if they are in main/restricted, also considers alternative dependencies, and create a report with a few hints.

For a main package where everything is alright, it looks like this:

$ check-mir 
Checking support status of build dependencies...

Checking support status of binary dependencies...
All dependencies are supported in main or restricted.

Example output for a totally synthetic situation with universe dependencies, non-preferred alternatives in main, and other special cases:

Checking support status of build dependencies...
 * pmount binary and source package is in universe
  ... alternative libexif-dev is already in main; consider preferring it
 * weechat binary and source package is in universe
 * sendmail-bin is in universe, but its source sendmail is already in main; file an ubuntu-archive bug for promoting the current preferred alternative

Checking support status of binary dependencies...
 * wesnot does not exist (pure virtual?)
 * wesnoth binary and source package is in universe

Please check https://wiki.ubuntu.com/MainInclusionProcess if this source package needs to get into in main/restricted, or reconsider if the package really needs above dependencies.

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Creating an HTTPS server in Python

For a test suite I need to create a local SSL-enabled HTTPS server in my Python project. I googled around and found various recipes using pyOpenSSL, but all of those are quite complicated, and I didn’t even get the referenced one to work.

Also, Python has shipped its own built-in SSL module for quite a while. After reading some docs and playing around, I eventually got it to work with a remarkably simple piece of code using the builtin ssl module:

import BaseHTTPServer, SimpleHTTPServer
import ssl

httpd = BaseHTTPServer.HTTPServer(('localhost', 4443), SimpleHTTPServer.SimpleHTTPRequestHandler)
httpd.socket = ssl.wrap_socket (httpd.socket, certfile='path/to/localhost.pem', server_side=True)
httpd.serve_forever()

(I use port 4443 so that I can run the tests as normal user; the usual port 443 requires root privileges).

Way to go, Python!

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