June 1, 2008
Blogroll, GNOME, General, PyGTK, Python, olpc
7 Comments
This was also sent to gtk-devel today:
== Introduction ==
GObject-introspection is a package which will collect and extend the API
metadata for GObject based libraries. The main motivation of this work is to
centralize all introspection information required to write a language binding.
There are many other use cases as well, some of them are described at:
http://live.gnome.org/GObjectIntrospection/
== Current status ==
The GObject-Introspection module/tarball contains the following:
* An XML format called GIR containing introspection information
* python package to create and parse the GIR format
* scanner to generate GIR format from C source and headers
These components are also included, but needs to be ported to the GIR format:
* a typelib similar to xpcom/msole which stores the information
on disk in a binary format
* a compiler to compile the typelib from a xml format (and vice versa)
* C library to read the typelib
A separate SVN module called gir-repository has been created.
The idea is to create .gir files of all libraries available in the
the whole stack which language bindings can depend on.
Eventually the plan is to move the .gir files into the upstream projects
themselves, but that’s likely to be a long process.
== GIR XML Format ==
The core of the GObject-introspection is an XML format which is called GIR (
GObject Introspection Repository) which contains the API introspection
metadata for a library or interface entity.
GIR currently contains three different XML namespaces:
- core: contains features available in popular programming languages: classes, methods, functions, interfaces, properties, strings, enums etc.
- c: contains features specific to the C language: identifiers, symbol names, C types
- glib: contains features specific to GLib/GObject: signal, GType, flags, paramspec
The separation of different data in different namespaces allow you
to reuse it allows you to arbitrarily extend the metadata available
in different languages.
== Scanner ==
To be able to bootstrap the effort and make something which will be
available in a reasonable timeframe we’ve been working on a scanner
which parsers C sources and headers and extracts the metadata and
generates a GIR file.
This is likely to be used by most of the Gtk/GNOME stack, as it would
require the least amount of work, however it’s not the only way to
use the GIR format nor GObject-Introspection.
In the future we might use something similar to CORBA IDL to define
the interface, as GIR is not meant to human editable.
In addition to the parsing the C headers, additional metadata will
be provided, likely by using source annotations in gtk-doc comments.
== Typelib ==
To be able to create efficient read introspection data we need a typelib, eg
an efficent disk format with a C API to access the internal data.
Matthias wrote one based on the XPCOM typelib which has not yet been
updated to the GIR format, it’s instead the tools to compile it are still
using an older XML format.
The work on finishing the typelib is depending on having the GIR format
somewhat stable and at that point updating the existing tools to understand it.
== How can I help? ==
At this point I’d like to get more eyes at the current GIR format to make
sure that it contains the necessary information and in a way which will
be easy to parse/access.
I am currently working mainly on the scanner to be able to quickly get
a large amount API expressed in GIR files.
For more information, check out the wiki page:
http://live.gnome.org/GObjectIntrospection/
And the gobject-introspection and gir-repository modules in GNOME SVN.
May 6, 2008
GNOME, General, PyGTK, Python, olpc
19 Comments
I have the pleasure of knowing the great mpt. He actually spent a couple of months in Brazil back in 2006 and we ended up sharing the same apartment during this period. One of the great things he masters is the art of writing ascii art mockups of user interfaces As I am a mere beginner might not be the best person to explain this. However I will make an attempt to explain the basic principles, in the effort of having this written down somewhere.
In this blog post I will focus on commonly used interactive widgets available in Gtk+, since these are the ones I tend to care the most about.
GtkEntry
An entry is straight forward, you use brackets in the beginning and the end and underscores to fill up the allocated width of the widget:
[____________]
If you want a text, just replace the underscores with letters
[Hello World____]
GtkButton
Buttons are similar to entries, the main difference is the lack of underscores and the use of capital letters. Icons are usually ignored as they often are rather tricky to represent using the ASCII alphabet. A cancel button looks like this:
[ CANCEL ]
GtkToggleButton and GtkRadioButton
Toggle buttons uses brackets around the toggle part and no brackets around the rest. If the value of the radio should be active, use a lowercase x to say so:
[ ] Buy milk and cheese for breakfast
[x] Eat strawberries after lunch
Radio buttons are similar but uses parenthesis and o, eg:
(o) Fresh fish
( ) Rotten eggs
GtkSpinButton
Spin buttons are similar to entries, but they have two small arrows on the right hand side. To represent the arrows, use H:
[1234 H]
This might not look good in all fonts, but it’s the best that can be done, at least as far as I know.
GtkComboBox
A combobox tend to be represented again by using brackes in the beginning and the end. To represent the arrow, use a lower case v and separate it from the text by using a | (pipe) sign.
[ Stockholm | v]
GtkDialog
Prett simple, use _ (underscore) and | (pipe) for the borders, titles and window manager buttons can usually be skipped since they are mostly noise to us in this context:
________________________________
| |
| Do you want to close the open |
| document and lose the changes |
| made to it? |
| [ CONTINUE ] [ QUIT ] |
|________________________________|
These are the widgets I usually end up using in my mockups. Have any missed any important onces? Or I have I done any serious mistakes? Comments appreciated!
Read the rest…
May 6, 2008
GNOME, General, PyGTK, Python
4 Comments
I often end up reading code using GtkListStore in Python, either in existing projects or on irc when someone asks me to fix their program. It’s pretty straight-forward to using the GtkTreeModel interface and it’s various implementations such as GtkListStore and GtkTreeStore. However, due to lack of proper documentation, the small pieces of Python sugar on top of the raw C wrappers is seldomly used. In this blog post I will attempt to document the most useful one in hope that some popular search engines will pick this up and help someone in the future.
Construction
For starters, let’s look into construction of GtkListStores:
model = gtk.ListStore(gobject.TYPE_STRING, gobject.TYPE_INT, gobject.TYPE_FLOAT)
This creates a liststore with three columns, a string, an integer and a float. The column types are specified using the constants available in the gobject python module. Since I’m hardly a normal person, I’ll immediatelly get frustrated when I see that kind of code. Instead, I wish people could write the following code instead, which is shorter and thus easier to parse:
model = gtk.ListStore(str, int, float)
It does exactly the same things, interally str is mapped to the gobject.TYPE_STRING constant and so on.
Appending data
At some point during the life time of a program you want to insert data into a model. A common way of doing is that is
the following:
iter = model.append()
model.set(iter, 0, “foobar”)
model.set(iter, 1, 1138)
model.set(iter, 2, 3.14)
This appends a new row and sets the values”foobar”,1138 and 3.14 to the three columns. You can avoid the three different calls by sending in a list to append as the first argument, eg:
model.append([”foobar”, 1138, 3.14])
Which again, is the exact same thing. (Modula saving a reference to the inserted tree iter of course)
Fetching values
To fetch a value from the a model you usually get an iter, for example from a selection:
model, path = selection.get_selected()
value = model.get_value(model.get_iter(path) , 0)
Two things can be simplified here: First of all we take advantage that model implementes a list like api, you can just access the model list a list, eg: model[n]. Secondly you can send in either an index, path or iter as n, so the example above is simplified to:
model, path = selection.get_selected()
value = model[path][0]
Iteration
Iteration over all the values in the model is usually done something like this:
iter = model.get_iter_first()
while True:
value = model.get_value(iter, 0)
iter = model.iter_next(iter)
if iter is None:
break
Which can also be considerably simplified:
for row in model:
value = row[0]
Also note that using the variable name iter in a python program is always wrong, since there is a builtin variable with the same name. Avoid the name iter, and use for instance titer instead, which is almost as short and a bit clearer.
May 5, 2008
General
1 Comment
Last week was not a very good one, at least not accident wise.
On Monday evening (a week ago today) I went to the bakery to get some bread and juice. Our poor dog hadn’t been out for a walk for a day or two so I decided to take her with me. Olivia is a 5 years old boxer who has been with us at the company for a long while, she’s very obedient and she’s free to run on the sidewalks without using a leash. She was very happy to go and ran off quickly, sticking to the sidewalk without entering the street. I walked by and let her run by herself. As we approached the first crossing she forgot, in a moment of joy to look at me if it was okay to pass the street and she ran over. Usually this kind of mistakes just end up with me telling her off. This was not her lucky day, a car approached and ran right into her. Luckily the car was not running very fast and the driver quickly hit the breaks. Olivia was not actually ran over, but she got up on her two legs and ran back towards the office without giving a sound. At this point I did not know if she was injured or not, so I started to run after her. A moment later, when I came back the office she wasn’t there. I spent the next two hours on my bike driving around the city trying to find her. Eventually through a couple of leads by pedestrians I could locate her in a corner about a km from where the accident had occurred. She was quickly brought to the vet would could only establish that she was well and had nothing broken. She had a couple of her pads on her front feet torn off, probably due to the shock and had a bit of pain walking. Today a week later she’s just fine, like nothing happened.
My second traffic incident of the week occurred when I came back after a 60km bike ride on Saturday evening. My Saturdays afternoons/evenings are reserved for bike riding and last week wasn’t an exception. We tend to leave around 14 and are seldom back before the sunset. When we came back on saturday it was not completely pitch dark, but it wasn’t many minutes of brightness left. As out of no where, a white VW Beetle overturns me, giving me approximately 2 m for me to either break or turn. Obviously I ran into the car with my front wheel, lost balance and smashed the asfalt pretty badly. My helmet cracked and the jersey got thorned apart, no serious injuries, just abrasions. What upset me the most was the fact that while the driver stopped to check if I was okay, he refused to acknowledge any wrong doing, merely telling me that “I couldn’t see you”. I will take it a lot easier in the future, especially when riding in darkness and cities. Moral of the story, as a cyclist, do not ever trust other drivers when riding in urban areas.
January 4, 2008
Blogroll, GNOME, General, PyGTK, Python, olpc
3 Comments
Yesterday I released two new releases of PyGObject and PyGTK. The most important change in both of releases is the support of a new API, available only in the svn version of Python which will prevent gobject and gtk from waking up once every 100 ms.
This should allow the CPU to be idle longer and thus save battery life, for your desktop and for children.
I would like to thank Guido van Rossum, Adam Olsen and Gustavo Carneiro for making sure that Python has enough support for this to be possible.
Unfortunately, it will take some time before this is widely used because it will only be included in Python 2.6. However, for OLPC the best option is probably to apply the patch from python issue 1583. Perhaps Linux distributors could do the same?
November 30, 2007
Blogroll, GNOME, General, PyGTK, Python, olpc
13 Comments
First of all, let me show you a screenshot showing what have been hacking on in my spare time over the last two weeks or so:
.
It’s showing a simple web browser written in python using WebKit, this is the code for that:
import bank
import Gtk, WebKit
win = Gtk.Window(Gtk.WindowType.TOPLEVEL)
p = WebKit.Page()
p.open(”http://www.google.com/”)
win.add(p)
win.show_all()
Gtk.main()
There are no specific bindings for WebKit, or even Gtk in this case. It’s all done using the introspection information available through gobject-introspection. I am not using the existing python bindings for GObject and GTK, I am instead using pybank, the python bindings for gobject-introspection.
The bank module, our interface to pybank differ from most (all?) GNOME language bindings written today by constructing the bindings in runtime. The bank module loads and interprets the metadata repository compiled using the g-idl-compiler tool. When you first access the Page class in WebKit it generates the Page class, and because it’s a GtkContainer subclass it imports the Gtk bindings and eventually the GObject ones as it’s also a subclass of GObject. When calling the constructors and methods it’s using libffi.
Before you’re all getting too excited, this is just a proof of concept, you won’t be able to build real applications based on pybank, you can’t even listen to signals yet. The only supported parameter types at the moment are int, str, enum and object. It’s mainly used a testcase for the introspection framework, to be able to make sure that the information available through introspection is going to work for this kind of language/binding.
The idea behind gobject-introspection is that each C library itself will generate and install the metadata at compile time. The metadata represents what you see in the C headers and a little bit extra which is already available through introspection in GObject such as properties, signals and class inheritence.
So what’s missing before we can start using this?
Jürg of Vala fame has written a header parser which will generate the metadata by scanning the headers. It’s in a pretty good state already, but not good enough to generate good enough metadata, it still needs to be tweaked a bit. The metadata in gobject-introspection needs a few additions such as typedefs, default values, a module/metdata mapping and a few other things.
In the screenshot attached below you can see that this is using about 6M of memory. Right, the bindings are not finished and the application is rather trivial, but I don’t expect this to go up significantly as I add more features for pybank, I expect it to go down as I can remove a couple of dependencies when gobject-introspection will be nearer to competition.
GObject-introspection goals:
- Provide all information necessary to generate language bindings
- Consolidate this information, to avoid duplication between all languages
- Encourage upstream projects to include the metadata
October 16, 2007
General
6 Comments
Mono
I’ve seem to have been the latest victim of this. That’s the sickness and not the software. I got the diagnosis last Friday, It’s likely that I’ll have a rough couple of months ahead of me.
Sweden
I’m back home in Sweden since a few weeks. I’ve not been able to enjoy it too much due to sickness.We will have to wait and see what the future holds for me. It’s great to see my family again, it’s been a while.
All seems so strange, like I’m gotten used to the South American way of doing things. I’m still amazed that I don’t need to lock doors when going out to the super market.
Vista
I haven’t been using windows more than a couple of minutes at a time since Win98/NT4. I bought a new laptop and it has Vista included. I don’t think it’s as bad as everyone says. There are a couple of very nice features. The volume mixer “applet” works surprisingly well. The main slider widget changes the volume on all channels/tracks instead of a predefine one (such as PCM/master/mumbo-yumboJ34). Why aren’t we doing something similar in GNOME, can’t be that hard..
August 8, 2007
Blogroll, GNOME, General, PyGTK, Python, olpc
4 Comments
This blog post will give you an introduction to the ObjectList widget which is a part of the kiwi library.
* Rationale
Creating graphical user interfaces which displays a sequence of objects is a common task. In the GTK+ toolkit you will normally use a GtkTreeView for this. GtkTreeView is a very flexible and extensible widget, for instance it allows you to separate the data storage from the representation. However the disadvantage of using the GtkTreeView is that it’s a little bit too complicated to use, especially for beginners.
The ObjectList aims to provide a familiar API to create, manipulate and access sequences of objects. It builds on top of GtkTreeView, and allows you to access the “raw” objects (view, columns, model, cellrenderers, selection) in case you want to do something which is not directly supported by the ObjectList.
Kiwi and ObjectList are tied to the Python programming language and depends heavily on PyGTK (and thus CPython). However the concepts introduced in the widget are usually not specific to Python, it’s very possible to implement similar high level wrappers on top of GtkTreeView for C#, Java etc.
* Simple ObjectList example
Here is the source code and the output of a simple ObjectList example
Let’s walk through the example and explain what it does.
- The class Fruit is defined with two attributes; name and price.
- An ObjectList called fruits is created which has two columns, name and price
- 5 objects are created and inserted into the list.
The example is concluded by creating a PyGTK window, adding the objectlist to it and running the main loop.
The data displayed in the ObjectList is stored in normal python instances, there is no need to create and set column types for a GtkTreeModel and extract the data from your python objects and insert it into the model. The model / view separation is kept while still keeping it easy to use.
Notice that the data is appended to the list by calling the append() method of the ObjectList, this is intentionally similar to the append method of the builtin list type of python. If you wanted you could use the extend() method to insert a list of object at one go.
The objects inserted into the list can be modified by using standard python list concepts:
- iteration: for item in list
- accessing an individual item: list[n]
- removing an item: del list[n] or list.remove(item)
- accessing parts of the item: list[n:m]
There are also methods beyond a normal python list routines which only makes sense in graphical interfaces:
- selecting an item: list.select(item)
- getting the selected item: list.get_selected()
- changing the columns: list.set_columns(columns)
- getting the columsn: list.get_columns()
- etc…
* Columns
When you create a column you define how the data is going to be displayed. Column width, sorting, justification, markup and so on. Here is an incomplete list of the support column attributes:
- title: the text will be used in the column header
- justify: the justification, eg left or right aligned
- format: printf style format string
- width: width in pixels of the column
- sorted: if we should sort the data after the content in this column
- editable: is the column editable?
- use_markup: should the content be interpreted as markup?
- use_stock: treat the content as stock icon names and display icons
Here is a more complicated, real world example from Stoq, a Retail Management System written on top of Kiwi.
The interface shows the accounts payable application which lists outgoing payments.
What we can see from the screenshot is:
- The first column is sorted and it has the title “#”
- The third column is the supplier name which is a bit too wide to fit and uses ellipsize
- The fourth column is the date the purchase was sold and is formatted according to the current locale
- The last column uses the special datatype currency which formats a number according to the monetary rules defined for the current locale, with thousand separators, decimal points and currency symbols set right.
This is all for now, for more information about Kiwi check out Howto, the API reference and the source code repository
August 6, 2007
General
2 Comments
Spammers have recently hit GIMPnet, the IRC network which hosts many GNOME and Mono related projects. Only a few channels are affected: #gnome, #gimp, #gtk+, #pygtk and #mono. The spamming has forced us to set the invite only flag, which prevents the spam bots from entering the channels and thus avoiding the spam. The downside of this is that no new users can enter these channels.
However, there’s a workaround, if you want to enter any of these channels just ask our friendly bot dorito to invite you, which can be done by sending him a private message, in most clients you can do this by typing:
/msg dorito invite #channel
If everything goes well you’ll receive an invitation to the channel. This has to be done each time you login to the network.
A long term solution is being worked on, this is just a temporary workaround.
June 24, 2007
Blogroll, GNOME, General, PyGTK, Python
8 Comments
Yesterday I on a bus ride from São Paulo I had the opportunity to see some of the developments tools available on OSX. Shark and mallocdebug are quite interesting, bling-bling for the developer masses.
When I woke up this morning I realized that it shouldn’t be too difficult to do something similar on top of valgrind.
[…later in the evening and 500 lines typed down…]
It’s quite useful already, it groups all the leaks by the topmost function which is a bit easier to follow than the output valgrind usually gives us.
You can find a tarball here if you want to play around with it.
Update: I uploaded a bzr branch to launchpad:
bzr branch http://code.launchpad.net/~jdahlin/andvare/main/
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