A few days ago someone said something[1] that reminded me about my audio player, which I had abandoned for more than a year already. The reason was mostly that the two Phonon backends, VLC and gstreamer, for some reason or other couldn't play the files I had without any gaps between songs.

To be honest, the first bug end up being me not properly encoding the filenames. If you first URL-encoded the filename and then built a Q/KURL with that, then it's all fine. It took me more than 12 months and a few rereads of the thread to realize it. Fixes apart, it seems that the bug still exists for other instances of gstreamer errors, so we're not out of the woods. In any case, I switched to the VLC backend and it seems that now is able to fire the aboutToFinnish() signal properly, so for the moment I'm using that.

All that is fine, but that's not what I wanted to talk about in this post. Given that this project largely precedes my interest on testing, it has no testing at all. Most of the project is straightforward enough to almost no need any, but there's a critic part that would not suffer at all if it had any, namely the Collections handling, including passing files from one to another and automatically updating new/removed Songs[2].

So after fixing the bug mentioned above I tried to figure out the current state of affaires regarding Collections, and boy, they're in bad shape. The code was locally modified, never commited, deactivating any notifications of filesystem changes (new or removed files), and other code I can't really understand the purpose of.

Because if this last detail is that I decided to start testing three classes: Collection, which handles a set a Songs with a common root directory; CollectionAggregator, which handles a set of collections and should coordinate moving a Song from one Collection to another; and CollectionIndexer, which scans from a Collection's root dir to find Songs.

All went fine while I tested the first class, Collection. There was a tricky part where I had to setup a QApplication in order to make signals work. The problems began when I started testing CollectionIndexer. Tests started blocking endlessly, signals stopped being either emited or firing the connected slots, life was bad.

I tried to search the available documentation and mailing lists for a hint about the problem, but besides a quite complex example that didn't seem to properly converge to anything useful, I was mostly on my own.

This morning I got my eureka moment: I noticed that if I executed each test class by itself, it worked, but both at the same time blocked and never finished. Then I remembered something said in QApplication's documentation:

For any GUI application using Qt, there is precisely one QApplication object, no matter whether the application has 0, 1, 2 or more windows at any given time.

That was it: I was creating the application, first in the setUp() method, then as a class attribute, but I had one test class per class to test, each in its own file. Somehow this last fact lead me to think that somehow they were executed in separate processes, which is not true. Luckily, even with this limitation, there's none on the amount of times you can exec_() and quit() the same instance, so that's what I did: I created only one instance and reused it everywhere. I was already doing that for each test method, but again, somehow having several files mislead me to think they were isolated from each other.

So now all my unit tests work without mysteriously blocking forever. Now I just hope I can keep riding the success wave and bring satyr into good shape. A new release wouldn't hurt.


[1] No matter how much I try, I can't get any vaguer.

[2] Ok, maybe the Player/Playlist combo wouldn't hurt to have UTs either.


satyr pykde python

Posted Mon 13 Oct 2014 02:22:53 PM CEST Tags: satyr

After several months thinking about it, and just two requests, I finally decided to publish satyr's code. I decided to use github because I already switched to satyr from hg to git, mainly for testing and understanding it. I think I can live with hg, althought branch management in git seems to be given more thought and a good implementation.

So, without further ado: satyr in github

Remember, it's still a test software, by no means polished or ready for human consumption, and with very low development force. Still, I think it has some nice features, like interchangeable skins and a well defined backend, D-Bus support, quick tag edition, reasonable collection managment, and, thanks to Phonon, almost-gapless playback and things like «stop after playing the current this file» (but not «after any given file» yet).

In Debian Sid it mostly works only with the GStreamer backend; I haven't tried the xine one and I know VLC does not emit a signal needed for queueing the next song, so you have to press «next» after each song. AFAIK this is fixed upstream.

satyr pykde python

Posted Sat 03 Sep 2011 02:59:43 PM CEST Tags: satyr

satyr-0.3.2 "I should install my own food" is out. The Changelog is not very impressive:

  • We can save the list of queued Songs on exit and load it at startup.
  • The queue position is not presented when editing the title of a Song that is queued.
  • Setting the track number works now (was a bug).
  • Fixed a bug in setup.py.

but the last one is somewhat important (Thanks Chipaca). Also, 2 months ago, I made the satyr-0.3.1 "freudian slip" release, when user 'dglent' from http://kde-apps.org/ found a packaging bug. It was not only a bugfixing revision, it also included new features:

  • nowPlaying(), exported via dbus.
  • 'now playing' plugin for irssi.
  • Changes in tags is copied to selected cells (in the same column). This allows 'Massive tag writing'.
  • Fixed "NoneType has no attribute 'row'" bug, but this is just a workaround.
  • Forgot to install complex.ui.

Now go get it!


satyr pykde python

Posted Wed 24 Feb 2010 10:16:41 PM CET Tags: satyr

One of the features I planned for satyr almost since the begining was the possibility to have 'skins'. In this context, a skin would not only implement the look and feel, but also could implement features the weren't available in the shipped classes. I also planned to implement this feature after I had most of the others one already done. But then I was bored this weekend with nothing to do and I decided to set off to at least investigate how to do it. Of course, what happened was that I implemented it almost completely.

Up to now, satyr's user interface was implemented in two files: default.ui, which was compiled with pyuic4 into default.py, and some code in satyr.py itself. This of course would not scale, and I always had the idea of moving the behaviour implemented in satyr.py to a file called default.py and load the ui directly from the default.ui file without compiling, getting rid of the need for a compilation at the same time. This also meant that then a skin would consist of a .py file and possibly a .ui file. There are three problems to solve for this: getting the local-to-the-user's skin directory, loading the skin and loading the correspondant .ui file.

The first part is simple from the PyKDE4 point of view:

# get the app's dir; don't forget the trailing '/'!
appDir= KStandardDirs.locateLocal ('data', 'satyr/')

I'll first explain the other two parts, loading the skin and the .ui file, before returning more deeply to the consequences of this solution.

I put all the skins in a skins subdirectory. To make it a proper python module I added an empty __init__.py file. Now, I could simply import skins.<skinName> and possibly instantiate some class in it, but of course one cannot write that. I could resort to eval ('import skins.'+skinName), but we know that eval() has the most long-standing typo in the history of computer languages, and it's actually called evil().

What we can do is resort to __import__() instead. This little function does approximately what we want. I say approx because it has some surprises in the sleeves of its sleeveless code. I suggest you to go read carefully its documentation. Meanwhile, the magic itself:

mod= __import__ ('skins.'+skinName, globals(), locals(), 'MainWindow')
mw= mod.MainWindow ()

Loading the .ui file in the skin's code is rather simple: just get the skin module's filepath, replace .py with .ui, and load it with PyQt4.uic.loadUiType()[1]. This function returns a generated class for the topmost widget and its Qt base class. This generated class has a setupUi() method that is the one that actually builds de UI[2]. So, we just instantiate the main window's class and call its setupUi() method:

from PyQt4 import uic

# !!! __file__ might end with .py[co]!
uipath= __file__[:__file__.rfind ('.')]+'.ui'
# I don't care about the base class
(UIMainWindow, buh)= uic.loadUiType (uipath)

self.ui= UIMainWindow ()
self.ui.setupUi (self)

Note the comment about the __file__ attribute of a module.

Now, and back to the first part, finding the local-to-the-user's skin directory is the easiest part. From there, things get a little bit more complicated:

  • The skins subdirectory might not exist.
  • If you create it, you gotta make sure to also throw in a __init__.py file.
  • Once you've done it, you also need to add the local-to-the-user's app directory to the path. It's easy, just prepend it to sys.path, so it's used before any system-wide directory.
  • The last problem that remains is exactly that: once the __init__.py is there and the user's dir is prepended to sys.path, the user's local skin directory is always used when importing anything from the skins module, so if a skin is not there it is not loadable. All skins distributed with satyr will be inaccesible!

So I'm in a kind of dead alley here. I have a couple of ideas on how to work-around this, but they're at best hacky, and I don't want to implement them until I'm sure that it's inevitable.


satyr pykde python


[1] Not a very happy name, if you ask me.

[2] Very similar to what you get if you compile the .ui with pyuic4.

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr

I certainly hope this is the last post in the Phonon-and-badly-encoded/mixed-encodings-filenames saga, but I know is just wishful thinking: as all encoding-related problems they never really dissapear, it's just that you hadn't hit the right wrong stone yet. In any case, I fixed all my later problems wherever they where, and now I can answer this question: how to play files whose filenames are badly encoded and/or have mixed encodings, all this in Phonon?

Right now the answer is: you have to provide a properly encoded QUrl. How, you might ask, can I get one of those? Are they selled in the same odly-looking places where you can buy cigarretes, or even marihuana[1]? The answer, luckly, is way more simple.

Putting together all the code I've been showing about Python, PyQt4/PyKDE4 and Phonon recently, it comes down to this[5]:

# path is a str()
qba= QByteArray (path)
# the exceptions are not needed,
# but is cleaner if you print the outcome of this
qu= QUrl.fromEncoded (qba.toPercentEncoding ("/ "))
# this is needed by the gstreamer backend[3],
# and the xine backend doesn't complain
qu.setScheme ('file')

... and that's it. You can now create a MediaSource with this qu.

There are a couple of ideas that I want to express as conclusion to all this:

  • In an ideal world these things should not happen. But this is one of the lesser problems with this non-ideal world, so bear with it.
  • Paths should not be stored in QStrings, even if they can (and they do) store this kind of pathnames, because if you try to 'encode' its contents (in the Unicode sense; that is, convert it to an encoding like UTF-8[4]) you get farts or barks at best. Yes, you always have constData() but from QString's class reference there is no warranty that this will keep being the case[6].
  • In fact, QString's class reference says at some point: «[one case] where QByteArray is appropriate are when you need to store raw binary data...», and [as I already wrote](http://grulicueva.homelinux.net/~mdione/glob/posts/from-qstring-to-bytes- in-pyqt/), «[t]his would be the case for paths; you need the bytes».
  • QFile and QDir can only be created from QStrings. I'm not sure if, given all I wrote, that's right.

The good news is that satyr now can play any file that the backends can whatever their filename-as-string-of-bytes is, I'm a little bit happier about it, I got another contribution to KDE and might even have to close a lot of bugs!


satyr pykde python phonon


[1] That question is only legal in Nederlands[2] and very few others cities in the planet.

[2] Actually is not legal. See [this wikipedia article](http://en.wikipedia.org/wiki/Drug_policy_of_the_Netherlands#Non- enforcement).

[3] I might pull up my sleeves again and fix that.

[4] You might have already know this, but if you not: you cannot print Unicode, because Unicode is not and encoding. You have to encode it first. Hence, the toLatin1(), toUtf8() and similar QString methods, and also the inverse from*().

[5] Of course the equivalent C++ code also works, with path being a char *.

[6] And in the case of PyQt4, that method is not even available. But [I already globed about it](http://grulicueva.homelinux.net/~mdione/glob/posts/from-qstring-to-bytes-in- pyqt/).

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr

For a couple of months I've been globbing about PyKDE4 stuff, and laterally talking about my last project: satyr. satyr (it's name should always be written in lowercase) should have the following features:

  • The PlayList and the Collection(s)[0] are the same thing.
  • Yours is a Collection of Albums, nothing else[3].
  • Some Albums are from the same artists and some are compilations[3].
  • If you want an ephemeral playlist you could queue songs[1].
  • If you want non-ephemeral playlists, then this player is not for you.
  • Ability to search à la xmms, but in the same interface[2]
  • Tag reading and writing[3].
  • Order you collection based on the tags[3].
  • The collection discovers new files and adds them to the playlist on the fly[4].
  • Be able to use all the program only with your keyboard (die, mouse, die!)

This and other features should be available soon. The coding has been fast lately, mainly because the Qt/KDE libs are fantastic to work with. The only thing I couldn't do was to read the tags before playing them, so I relied into the kaa libraries.

The project is hosted in savannah, and right now there is no tarball (It's marked as alpha state because I sent a couple of tarballs to some friends who asked for them), so the only way right now is to branch anonimously the bazaar repo. I hope you download and enjoy it as much as I do.

satyr pykde


[0] The support for several collections is not complete yet.

[1] Functionality available via dbus only at the moment.

[2] This is with the current GUI. I'm also thinking in several/pluginable GUI's

[3] Not yet available.

[4] Of course this only works if it's running. Otherwise, you can always ask for a rescanning[1].

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr

Update before even publishing: most of the numbers in the initial writing were almost doubled. The problem was that distutils left a build directory when I tried either to install or to package satyr, I don't remember which, so the files found by the find commands below were mostly duplicated. I had to remove the directory and run all the commands again!

I wanted to know some things about satyr's code, in particular some statistics about its lines of code. A first approach:

$ find . -name '*.py' -o -name '*.ui' | xargs wc -l | grep total
  2397 total

Hmm, that's a lot, I don't remember wrinting so many lines. Beh, the comments, let's take them out:

$ find . -name '*.py' -o -name '*.ui' | xargs egrep -v '^#' | wc -l
2136

What about empty lines?:

$ find . -name '*.py' -o -name '*.ui' | xargs egrep -v '^(#.*| *)$' | wc -l
1764

Meeh, I didn't take out all the comment lines, only those lines starting with #, which are mainly the license lines on each source file. I have to also count the comments in the middle of the code:

$ find . -name '*.py' -o -name '*.ui' | xargs egrep -v '^( *#.*| *)$' | wc -l
1475

And how much of those lines are actual code and not from some xml file describing user interface?:

$ find . -name '*.py' | xargs egrep -v '^( *#.*| *)$' | wc -l
1124

How much code means its 3 current skins?:

$ find satyr/skins/ -name '*.py' | xargs egrep -v '^( *#.*| *)$' | wc -l
341

How much in the most complex one?

$ egrep -v '^( *#.*| *)$' satyr/skins/complex.py | wc -l
182

All this numbers tell something: ~300 empty lines means that my code is not very tight. I already knew this: I like to break functions in secuential blocks of code, each one accomplishing a somehow atomic step towards the problem the function tries to solve. Almost 300 comment lines means my code is very well commented, even if a sixth of those comments are BUGs, TODOs, FIXMEs or HINTs:

$ find . -name '*.py' | xargs egrep '^ *# (TODO|BUG|FIXME|HINT)' | wc -l
56

Wow, more than I thought. Now, 1100 lines of actual code for all that satyr accomplishes today (playing almost any existing audio file format, progressive collection scanning, lazy tag reading and also tag writing, 3 skins[4], handle several Collections, searching, random, stop after, saving some state, picking up new songs added to the collection via the filesystem, queuing songs[1], dbus interface[2], handle any encodings in filenames[3]... phew! and some minor features more!) I think is quite impressive.

Of course, doing all that in athousandsomething lines of code would be nearly impossible without PyQt4/Qt4, PyKDE4/KDE (something) 4[7], Tagpy/Taglib and finally Python itself. It's really nice to have such a nice framework to work with, really.


satyr pykde python


[1] No user interface for this yet; shame on me.

[2] ... which toguether with kalarm and qdbus make my alarm clock.

[3] Almost all the support is in Phonon itself.

[4] [5] Less than 800 if we don't count skins.

[5] Yes, I add more footnotes as I readproof the posts :)

[6] I skipped [6] :)

[7] After the rebranding I don't know which is the proper name for the libraries, because I'm writing this post while very much offline, and TheDot does not publish the whole articles via rss, which I hate.

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr

Satyr handles paths. There are some problems with paths and (sigh) encondings. Of those, here are two: there's no way to know in which encoding the filenames in a filesystem are enconded (f.i., there's no way to ask the filesystem), and even if that were possible, the filenames might not even be enconded in that enconding. In these (still!) transitioning times, lots and lots and shitloads of filesystems are used in UTF-8 environments, but some filenames are still in old ISO-8859-1 or whatever the system was using before.

Then comes QString. I'm taking a path from the command line; this path is the location of the (right now only) Collection for the player. I'm handling the command line using KCmdLineOptions, which returns QStrings. As we all know, QString, just like the unicode type in Python, handles all the data internally as Unicode, which is The Right Thing™. If you really need the internal data, say as bytes, you can always call the constData() method and be happy with it[1]. This would be the case for paths; you need the bytes.

Then comes PyQt4. For some reason, which maybe I will ask in the pyqt devel ML[2], constData() is not available. What to do? Well, that's what this post is about. What you're about to read is hacky as it can be, but then it works. I might feel dirty, but I can live with it. As long as I mark it as a utter/über hack and promise to revert it once that's possible...

# path is a QString
qba= QByteArray ()
qba.append (path)
path= str (qba)
# now path is a list of bytes/string.

Even if this part of the bug is fixed, then Phonon.MediaSource or Phonon.MediaObject.play() fails when feeded that same path with this message:

ERROR: backend <span class="createlink">MediaObject</span> reached <span class="createlink">ErrorState</span> after  1 . It seems a <span class="createlink">KioMediaStream</span> will not help here, trying anyway.

or simply refusing to continue. Sure, in my case I should simply ignore the filename and inform the user what's going on, but sometimes you can't be so gentle.

satyr pykde python phonon


[1] blah.

[2] but then it doesn't make much sense now since Phil wants to get rid of QString (for several reasons, which might most possibly include this one).

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr

satyr got the possibility to queue songs for playing very early. At that moment there wasn't any GUI, so the only way to (de)queue songs was via dbus[1]. Once the GUI was there, we had to provide a way to queue songs. As satyr aims to be fully usable only using the keyboard, the obvious way was to setup some shortcut for the action.

Qt and then KDE have a very nice API for defining 'actions' that can be fired by the user. The ways to fire them include a shortcut, a menu entry or a button in a toolbar. I decided to go with the KDE version, KAction.

According to [the documentation](http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/ classKAction.html#_details), to create an action is just a matter of creating the action and to add it to an actionCollection(). The problem is that nowhere it says where this collection comes from. There's the KActionCollection class, but creating one and adding the actions to it seems to be not enough.

If you instead follow the tutorial you'll see that it refers to a KXmlGuiWindow, which I revised when I was desperately looking for the misterious actionCollection(). I don't know why, but the documentation generated by PyKDE does not include that method. All in all, the tutorial code works, so I just ported my MainWindow to KXmlGuiWindow:

class MainWindow (KXmlGuiWindow):
    def __init__ (self, parent=None):
        KXmlGuiWindow.__init__ (self, parent)
        uipath= __file__[:__file__.rfind ('.')]+'.ui'
        UIMainWindow, _= uic.loadUiType (uipath)

        self.ui= UIMainWindow ()
        self.ui.setupUi (self)
        [...]
        self.ac= KActionCollection (self)
        actions.create (self, self.actionCollection ())

and actions.create() is:

def create (parent, ac):
    '''here be common actions for satyr skins'''
    queueAction= KAction (parent)
    queueAction.setShortcut (Qt.CTRL + Qt.Key_Q)
    ac.addAction ("queue", queueAction)
    # FIXME? if we don't do this then the skin will be able to choose whether it
    # wants the action or not. with this it will still be able to do it, but via
    # implementing empty slots
    queueAction.triggered.connect (parent.queue)

Very simple, really. But then the action doesn't work! I tried different approaches, but none worked.

The tutorial I mentioned talks about some capabilities of the KXmlGuiWindow; one of them, the ability to have the inclusion of actions in menues and toolbars dumped and loaded from XML file (hence, the XML part of the class name), and that is handled by the setupGUI() method. From its documentation: «Configures the current windows and its actions in the typical KDE fashion. [...] Typically this function replaces createGUI()». In my case the GUI is already built by that self.ui.setupUi() that you see up there, so I ignored this method. But the thing is that if you don't call this method, the actions will not be properly hooked, so they don't work; hence, my problem. But just calling it make the actions work! I'll check later what's the magic behind this method. For now just adding self.setupGUI() at the end of the __init__() was enough.

So, that's it with actions. As a result I also get several things: a populated menu bar with Settings and Help options (but no File; that'll come later with standard actions, of which I'll talk about later, I think), with free report bug, about satyr and configure shortcuts options, among others. The later does work but its state is not saved. That also will come in the same post that standard actions.

PD: First post from my new internet connection. Will satyr suffer from this? Only time will tell...


satyr pykde python


[1] then you had to pick the index of the songs either by guessing or looking at the dump of the playlist.

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr

In my last post I said «The next step is to make my Player class to export its methods via DBus and that's it!». Well, tell you what: is not that easy. If you try to inherit from QObject and dbus.service.Object you get this error:

In [3]: class Klass (QtCore.QObject, dbus.service.Object): pass
<span class="createlink">TypeError</span>: Error when calling the metaclass bases
    metaclass conflict: the metaclass of a derived class must be a
    (non-strict) subclass of the metaclasses of all its bases

This occurs when both ancestors have their own metaclasses. Unluckily Python doesn't resolve it for you. The answer is to create a intermediate metaclass which inherits from both metaclasses (which we can obtain with type()) and make it the metaclass of our class. In code:

class <span class="createlink">MetaPlayer</span> (type (QObject), type (dbus.service.Object)):
    """Dummy metaclass that allows us to inherit from both QObject and
    d.s.Object"""
    pass

class Player (QObject, dbus.service.Object):
    __metaclass__= <span class="createlink">MetaPlayer</span>
    [...]

Is that it now? Can I go and do my code? Unfortunately no. See this:

qdbus org.kde.satyr
/
/player
Cannot introspect object /player at org.kde.satyr:
org.freedesktop.DBus.Python.KeyError (Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.5/dbus/service.py", line 702, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/lib/pymodules/python2.5/dbus/service.py", line 759, in Introspect
    interfaces = self._dbus_class_table[self.__class__.__module__ + '.' + self.__class__.__name__]
<span class="createlink">KeyError</span>: '__main__.Player'
)

This is the class dbus.service.Object complaining something else. It's getting late here and I'm tired, so I'll continue tomorrow.

dbus python pykde satyr

Posted Wed 27 Jan 2010 11:55:55 PM CET Tags: satyr