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{{Developers}}
The Pygame wrapper is called olpcgames. For a tutorial on how to use it, see [[Game development HOWTO]]. This is the reference manual.
<< [[API reference]]


{{Olpcboxtop|toptext=[[{{PAGENAME}}|OLPCGames]]}}
=Getting the wrapper=
{{ OBX source dev|projects/games-misc}}
{{ OBX devtickets |olpc-games}}
{{ OBX team |[[User:Mcfletch|Mike Fletcher]]}}
[http://dev.laptop.org/git?p=projects/games-misc;a=tree;f=olpcgames-src/dist;hb=HEAD Download]
{{Olpcboxbottom}}


''(See also [http://wiki.sugarlabs.org/go/Development_Team/Sugargame Sugargame].)''
Eventually, the wrapper will be a part of the standard build. Before then, you need to get it from Git:
git clone git://dev.laptop.org/projects/games-misc


The [[Pygame]] wrapper for the OLPC [[Sugar]] platform is called OLPCGames. This page explores the differences between standard Pygame programming and OLPCGames-mediated Pygame programming.
The 'olpcgames' directory is the package in question. Submodules you can access are activity, canvas, camera, and pangofont. The wrapper also replaces certain Python modules (python.event) with 'eventwrap' (which can also be imported separately), so we document those here too.


The automatically generated [http://dev.laptop.org/~mcfletch/OLPCGames/pydoc/olpcgames.html Pydoc documentation for OLPCGames] is the canonical reference work for the documentation.
=Notes and Reference=


=Strategic Rationale=
==Caveats==
The SDL Pygame wrapper allows for nested Pygame windows using a separate thread. It forwards GTK events and converts them to Pygame events. Games under the wrapper may not work exactly the same way and porting is not completely seamless -- you should be aware of a few OLPC-specific caveats:


The particular value of the OLPCGames wrapper is not, in fact, the ability to run Pygame games on the OLPC. The particular value is that by using Pygame for your game, and OLPCGames as your wrapper, you should not need to worry about the underlying details of the (rapidly changing, and rather breakage-prone) Sugar API.
* You cannot set the display mode using pygame.display.set_mode. You must set it in the wrapper boilerplate instead (see [[Game development HOWTO]]).


Historically that changing API has forced each (PyGTK) developer to revise their activities time and again. OLPCGames, which is effectively the "Sugar" side of your Pygame activity, is shared among many projects, so that when it is fixed, all of the games using it are fixed along with it (generally only needing to replace the version of OLPCGames they are using and re-publishing the .xo file).
* It is not recommended that you use the regular Pygame.font text drawing. You can use the wrapper to draw text using the 'olpcgames.pangofont' module instead which supports proper internationalization. See [[Pygame wrapper#Pangofont]].


In addition, there are platforms where creating a working Sugar development environment is a non-trivial task. For those environments, it is often possible to set up a simple Pygame environment, write your game/Activity in that environment, and then port (or have someone port) the Activity to the XO in a matter of minutes.
* The event module is shadowed by [[Pygame wrapper#Eventwrap]] and some methods may not work exactly the same. Certain methods in pygame.mouse and pygame.key are also shadowed.


=Tutorials=
* There's no CD-ROM, so the 'cdrom' module isn't useful.


* [http://www.vrplumber.com/olpc/pycon2008-handout.odt PyCon 2008 Tutorial] ([http://www.vrplumber.com/olpc/pycon2008.tar.gz Code]) -- Hello World, Participant Tracking in Games, Networked TicTacToe, Journal integration, SVG and Pango rendering
* The cursor is the small X cursor at this time. We should consider changing it to a standard Sugar cursor.
* [[Porting pygame games to the XO]] -- Phil Hassey's notes on porting two of his games to the XO. Much shorter and higher-level presentation, assumes you already have a working Pygame game, know your way around your game's code base, and just need to know what's different about OLPCGames under Sugar
* [[Game development HOWTO]] -- describes the process of building a new skeleton project
* [http://pygametutorials.wikidot.com OOP tutorial for PyGame]


=Getting the wrapper=
==Keyboard and Mouse==
Keyboard and mouse work. The "gamepad" buttons on the left and right of the screen come in as Numpad number keys (the d-pad is 8,2,4,6 and the buttons are 1,3,7,9).


You can either [http://dev.laptop.org/~mcfletch/OLPCGames/ download the wrapper] as a .zip or .tar.gz
==Other events==
Window resizing probably doesn't work well yet (i.e., resizing windows via the screen rotate button), but we will try to get this working soon.


wget http://dev.laptop.org/~mcfletch/OLPCGames/OLPCGames-1.6.zip


or you can check it out of the git repository on dev.laptop.org (note, do '''not''' attempt this on an XO or other space-constrained device, GIT downloads the entire history of the project, which is over 120MB in this case).
=Activity=


git clone git://dev.laptop.org/projects/games-misc
The <code>olpcgames.activity</code> module encapsulates creation of a Pygame activity. Your Activity should inherit from this class. Simply setting some class attributes is all you need to do in a class inheriting from olpcgames.activity.PyGameActivity in order to get Pygame to work.


The 'olpcgames' directory is the package in question. Submodules you can access are activity, canvas, camera, mesh, and pangofont. The wrapper also replaces certain Python modules (e.g. pygame.event with 'eventwrap' (which can also be imported separately)), so we document those here too.
<pre>
class PyGameActivity(activity.Activity):
game_name = None
game_title = 'PyGame Game'
game_handler = None
game_size = (units.grid_to_pixels(16),
units.grid_to_pixels(11))
pygame_mode = 'SDL'
</pre>


=Activities=
You need to set these:


The following Activities use OLPCGames and can serve as example code, (note that some of these projects may not be finished yet):
'''<code>game_name</code>''': This is a string containing the name of the module and, optionally a colon followed by the name of the main method (example: "tictactoe:main"). If there's no main method specified it defaults to "main". In this example, the wrapper code will import the module named "tictactoe" and call main() on it. That is expected to enter a Pygame main loop (which makes some call into pygame.event periodically, see [[Pygame wrapper#Eventwrap]]).


* [[Story Builder]] -- Environment for creating story modules to be used in [[MaMaMedia]], uses the PGU GUI library extensively
'''<code>game_title</code>''': This is the string containing the title of the game, as it appears in the Sugar toolbar at the top of activities.
* [[Games/Productive|Productive]] -- A Real-time Strategy game written explicitly for the OLPC platform. Includes networking via the mesh module (and raw Telepathy primitives). Graphics are via raw Pygame coding.
* [[Games/FiftyTwo|FiftyTwo]] -- A set of card games
* [[Maze]] -- Maze navigation game


* [http://dev.laptop.org/git?p=projects/games-misc;a=blob;f=cameratest.activity/run.py;hb=HEAD Camera Test] -- example of using the <code>olpcgames.camera</code> module [http://dev.laptop.org/~mcfletch/testactivities/cameratest-1.xo XO]
'''<code>game_size</code>''': Pixel resolution of your game window. This is not changeable at runtime. This needs to match whatever you pass to pygame.display.set_mode(), and you cannot call set_mode() later with a different size.
* [http://dev.laptop.org/git?p=projects/games-misc;a=blob;f=soundtest.activity/run.py;hb=HEAD Sound Test] -- example showing simple multi-channel sound usage [http://dev.laptop.org/~mcfletch/testactivities/soundtest-1.xo XO]


* [http://dev.laptop.org/git?p=projects/games-misc;a=blob;f=svgspritetest.activity/run.py;hb=HEAD SVG Sprite Test] -- example showing use of the <code>olpcgames.svgsprite</code> module [http://dev.laptop.org/~mcfletch/testactivities/svgspritetest-1.xo XO]
These are optional:


* [http://dev.laptop.org/git?p=projects/games-misc;a=blob;f=videotest.activity/run.py;hb=HEAD Video Test] -- example showing use of the [[GStreamer]]-based <code>olpcgames.video</code> module [http://dev.laptop.org/~mcfletch/testactivities/videotest-2.xo XO]
<code>pygame_mode</code> can be set to 'Cairo' if you want experimental Cairo pygame support. In this case you need to include 'pygamecairo' module accessible from your game. This is not recommended as Cairo is quite slow.
* [http://drupal.ceibaljam.org/?q=node/235 Quinteti] -- Tic Tac Toe like game [http://drupal.ceibaljam.org/sites/default/files/Quinteti-1_0.xo XO]


=Differences from Pygame=
<code>game_handler</code> is a deprecated synonym for game_mode.


The SDL Pygame wrapper allows for nested Pygame windows using a separate thread. It forwards GTK events and converts them to Pygame events. Games under the wrapper may not work exactly the same way and porting is not completely seamless -- you should be aware of a few OLPC-specific caveats:
=Canvas=

* You cannot set the display mode using pygame.display.set_mode. You must set it in the wrapper boilerplate instead (see [[Game development HOWTO]]).

* It is not recommended that you use the regular Pygame.font text drawing. You can use the wrapper to draw text using the 'olpcgames.pangofont' module instead which supports proper internationalization. See [http://dev.laptop.org/~mcfletch/OLPCGames/pydoc/olpcgames.pangofont.html Pangofont].

** ''NOTE'': If you are developing on an AMD64/EMT64 platform, there is a bug in Pygame 1.7.x which prevents it from working with the SVG or PangoFont modules. This bug has been fixed on the trunk of Pygame and should show up with the next release.

* The event module is shadowed by [http://dev.laptop.org/~mcfletch/OLPCGames/pydoc/olpcgames.eventwrap.html Eventwrap] and some methods may not work exactly the same. Certain methods in pygame.mouse and pygame.key are also shadowed.

* There's no CD-ROM on OLPC-XOs, so the 'cdrom' module isn't generally useful.

=Keyboard and Mouse=


Keyboard and mouse work approximately as they do under Pygame. We simulate repeated key-down events when a key is held down for a period in order to simulate Pygame's operation.
The canvas submodule handles wrapping events and initializing SDL inside the container.


The "gamepad" buttons on the left and right of the screen come in as Numpad number keys (i.e., <code>pygame.K_KP1</code> through <code>pygame.K_KP9</code>):
<pre>
<pre>
D-Pad (left of screen) Gamepad (right of screen)
class PyGameCanvas(gtk.EventBox):
pass
8 9 O
4 6 7 1 [] V
2 3 X
</pre>
</pre>


The D-pad (directional pad) mappings make sense as the traditional arrow keys on the numeric keypad of 101-key keyboards. The gamepad mappings make sense when you realize that 9/3 are page-up/page-down and 7/1 are home/end. The d-pad has 8 directions of articulation. You detect the diagonals by looking for two keys pressed at the same time.
There's nothing you probably need to interact with in the canvas submodule.


When designing your interfaces keep in mind that an OLPC-XO in tablet mode only has the eight "keys" above available (as well as a resize-and-rotate key, but that's already mapped by the operating system).
=Eventwrap=


Keep in mind that your activities will need to be localized into many languages, so binding, for instance "p" to "produce" is sub-optimal. If possible provide a run-time configuration, or at least a localization-time configuration mechanism (such as a configuration file) that lets more natural keys be chosen for each language's keyboard.
The 'eventwrap' module is a replacement for pygame.event. It has much of the same interface (see [http://www.pygame.org/docs/ref/event.html]). See the doc-strings of these methods for full documentation; I'll point out the differences here:


== OLPC-XO (B4) Hardware Notes ==
There is an install() method which installs eventwrap in place of pygame.event, so that unaware Pygame applications will use this event queue rather than the native Pygame one. Performance is mostly unaffected, and this event queue is more versatile than Pygame's. Thus, we do this for all Pygame games as part of the Activity wrapper.


The D-Pad control is usable for general control operations, but it is not a precise/fast control device as seen on gaming console controllers. It often slips from a cardinal direction to the adjacent intermediate direction (i.e. from left to left+up). You should not expect a traditional "platformer" game to be played with this control without some heuristics to clean up the input.
This event queue does not support getting events only of a certain type. You need to get all pending events at a time, or filter them yourself. You can, however, block and unblock events of certain types, so that may be useful to you. Set_grab doesn't do anything (you are not allowed to grab events). Sorry.


The checkmark button (K_KP1) is far easier to click than the X button, so "click" for "fire" should likely be the checkmark rather than the X. (Which makes sense to English users, at least). The Game pad buttons are small and close enough that asking a user to rapidly switch between them will likely result in a lot of multiple-button push events. Again, some heuristic code would be needed to clean up the input.
=Camera=


= Cursors =
<pre>
def snap():
"""Dump a snapshot from the camera to a pygame surface."""
</pre>


See [[Sugar Standard Icons]] for instructions on how to create and use a standard Sugar cursor within Pygame-based games. The arrow and hand cursor there should likely be sufficient for most games.
What it says. This method takes approximately forever, so it's not that useful right now. It takes a snapshot, saves it to a temporary file, and then loads the file as an image.


= Antialiased Lines =
=Pangofont=


The bit-depth chosen by the wrapper (16 bit on OLPC-XOs, normally) tends to make antialiased lines fail. The reason this is so hasn't been extensively investigated, so it's not known whether this is a hard-and-fast limitation, or just an optimization hint.
The 'pangofont' module is a replacement for pygame.font. It has a similar interface (see [http://www.pygame.org/docs/ref/event.html]). See the doc-strings of these methods for full documentation; I'll point out the differences here:


= Journal Integration =
There is an install() method which installs pangofont in place of pygame.font, so that unaware Pygame applications will draw with Pango rather than SDL_ttf (the default font backend in SDL). Unlike eventwrap, install() is not called automatically.


OLPCGames produces events to tell you about Journal save/restore requests:
The main problem with SDL_ttf is that it doesn't handle internationalization nearly as well as Pango (in fact, pretty much nothing does). However, it is fairly fast and it has a rich interface. You should avoid fonts where possible, prerender using Pango for internationalizable text, and use Pango or SDL_ttf for text that really needs to be rerendered each frame. (Use SDL_ttf if profiling demonstrates that performance is poor with Pango.)


*pygame.USEREVENT
<pre>
**code = olpcgames.FILE_READ_REQUEST (OLPCGames 1.6+)
class PangoFont(object):
*** filename -- the filename to be read
"""Base class for a pygame.font.Font-like object drawn by Pango."""
*** metadata -- metadata object (dictionary like)
def __init__(self, family=None, size=None, bold=False, italic=False, fd=None):
**code = olpcgames.FILE_WRITE_REQUEST (OLPCGames 1.6+)
"""If you know what pango.FontDescription (fd) you want, pass it in as
*** filename -- the filename to be written
'fd'. Otherwise, specify any number of family, size, bold, or italic,
*** metadata -- metadata object (dictionary like)
and we will try to match something up for you."""


which are generated to allow you to save/restore to/from the [[Journal]]/Datastore on the OLPC.
def render(self, text, antialias, color, background=None):
"""Render the font onto a new Surface and return it.
We ignore 'antialias' and use system settings.
NOTE: Due to a retarded implementation problem you cannot use
transparent colors. Alpha is ignored (set to 255)."""


= Window Resizing =
class SysFont(PangoFont):
"""Construct a PangoFont from a font description (name), size in pixels,
bold, and italic designation. Similar to SysFont from Pygame."""
def __init__(self, name, size, bold=False, italic=False):


Window resizing doesn't work yet (i.e., resizing windows via the screen rotate button), but we will try to get this working soon.
def fontByDesc(desc="",bold=False,italic=False):
"""Constructs a FontDescription from the given string representation."""


=Module Reference=

The [http://dev.laptop.org/~mcfletch/OLPCGames/pydoc/olpcgames.html pydoc-generated documentation] for the OLPCGames package serves as the canonical reference work at this point.

= Customizing the Toolbar =

If you want to add stuff to the standard toolbar you can override build_toolbar in your PyGameActivity subclass like this:

<pre>
import pygame
import olpcgames
from sugar.graphics.toolbutton import ToolButton
from gettext import gettext as _

...

def build_toolbar( self ):
"""Build our Activity toolbar for the Sugar system."""
toolbar = super( MyActivityClass, self ).build_toolbar()
# Add a button
mybutton = ToolButton('activity-mybutton') # put the icon file here: MyGame.activity/icons/activity-mybutton.svg
mybutton.set_tooltip(_('Something'))
mybutton.connect('clicked', self._mybutton_cb)
toolbar.insert(mybutton, 2)
mybutton.show()
return toolbar

def _ mybutton_cb(self, button):
pygame.event.post(olpcgames.eventwrap.Event(pygame.USEREVENT, action='mybutton'))
</pre>
</pre>


Then in your event handler do this:
The format of the fontByDesc string representation is passed directly to the pango.FontDescription constructor and documented at [http://www.pygtk.org/docs/pygtk/class-pangofontdescription.html#constructor-pangofontdescription]. Bold and italic are provided as a convenience. Example descriptions:


<pre>
"sans bold 12"
if event.type == pygame.USEREVENT:
"serif,monospace bold italic condensed 16"
if event.action == 'mybutton':
"normal 10"
self.dosomething()
else:
print "Unknown user event action:", event.action
</pre>


[[Category:Developing games]]
Note that PangoFont objects don't have any of the methods to mutate or examine the font (set_bold, get_line_height, etc.) that pygame.font.Font has. If you really need these methods, you can consider sticking with SDL_ttf.
[[Category:Python]]

Latest revision as of 20:33, 25 July 2013

<< API reference

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(See also Sugargame.)

The Pygame wrapper for the OLPC Sugar platform is called OLPCGames. This page explores the differences between standard Pygame programming and OLPCGames-mediated Pygame programming.

The automatically generated Pydoc documentation for OLPCGames is the canonical reference work for the documentation.

Strategic Rationale

The particular value of the OLPCGames wrapper is not, in fact, the ability to run Pygame games on the OLPC. The particular value is that by using Pygame for your game, and OLPCGames as your wrapper, you should not need to worry about the underlying details of the (rapidly changing, and rather breakage-prone) Sugar API.

Historically that changing API has forced each (PyGTK) developer to revise their activities time and again. OLPCGames, which is effectively the "Sugar" side of your Pygame activity, is shared among many projects, so that when it is fixed, all of the games using it are fixed along with it (generally only needing to replace the version of OLPCGames they are using and re-publishing the .xo file).

In addition, there are platforms where creating a working Sugar development environment is a non-trivial task. For those environments, it is often possible to set up a simple Pygame environment, write your game/Activity in that environment, and then port (or have someone port) the Activity to the XO in a matter of minutes.

Tutorials

  • PyCon 2008 Tutorial (Code) -- Hello World, Participant Tracking in Games, Networked TicTacToe, Journal integration, SVG and Pango rendering
  • Porting pygame games to the XO -- Phil Hassey's notes on porting two of his games to the XO. Much shorter and higher-level presentation, assumes you already have a working Pygame game, know your way around your game's code base, and just need to know what's different about OLPCGames under Sugar
  • Game development HOWTO -- describes the process of building a new skeleton project
  • OOP tutorial for PyGame

Getting the wrapper

You can either download the wrapper as a .zip or .tar.gz

wget http://dev.laptop.org/~mcfletch/OLPCGames/OLPCGames-1.6.zip

or you can check it out of the git repository on dev.laptop.org (note, do not attempt this on an XO or other space-constrained device, GIT downloads the entire history of the project, which is over 120MB in this case).

git clone git://dev.laptop.org/projects/games-misc

The 'olpcgames' directory is the package in question. Submodules you can access are activity, canvas, camera, mesh, and pangofont. The wrapper also replaces certain Python modules (e.g. pygame.event with 'eventwrap' (which can also be imported separately)), so we document those here too.

Activities

The following Activities use OLPCGames and can serve as example code, (note that some of these projects may not be finished yet):

  • Story Builder -- Environment for creating story modules to be used in MaMaMedia, uses the PGU GUI library extensively
  • Productive -- A Real-time Strategy game written explicitly for the OLPC platform. Includes networking via the mesh module (and raw Telepathy primitives). Graphics are via raw Pygame coding.
  • FiftyTwo -- A set of card games
  • Maze -- Maze navigation game
  • Camera Test -- example of using the olpcgames.camera module XO
  • Sound Test -- example showing simple multi-channel sound usage XO

Differences from Pygame

The SDL Pygame wrapper allows for nested Pygame windows using a separate thread. It forwards GTK events and converts them to Pygame events. Games under the wrapper may not work exactly the same way and porting is not completely seamless -- you should be aware of a few OLPC-specific caveats:

  • You cannot set the display mode using pygame.display.set_mode. You must set it in the wrapper boilerplate instead (see Game development HOWTO).
  • It is not recommended that you use the regular Pygame.font text drawing. You can use the wrapper to draw text using the 'olpcgames.pangofont' module instead which supports proper internationalization. See Pangofont.
    • NOTE: If you are developing on an AMD64/EMT64 platform, there is a bug in Pygame 1.7.x which prevents it from working with the SVG or PangoFont modules. This bug has been fixed on the trunk of Pygame and should show up with the next release.
  • The event module is shadowed by Eventwrap and some methods may not work exactly the same. Certain methods in pygame.mouse and pygame.key are also shadowed.
  • There's no CD-ROM on OLPC-XOs, so the 'cdrom' module isn't generally useful.

Keyboard and Mouse

Keyboard and mouse work approximately as they do under Pygame. We simulate repeated key-down events when a key is held down for a period in order to simulate Pygame's operation.

The "gamepad" buttons on the left and right of the screen come in as Numpad number keys (i.e., pygame.K_KP1 through pygame.K_KP9):

D-Pad (left of screen)             Gamepad (right of screen)
  
      8                                    9       O
    4   6                                7   1   []  V
      2                                    3       X

The D-pad (directional pad) mappings make sense as the traditional arrow keys on the numeric keypad of 101-key keyboards. The gamepad mappings make sense when you realize that 9/3 are page-up/page-down and 7/1 are home/end. The d-pad has 8 directions of articulation. You detect the diagonals by looking for two keys pressed at the same time.

When designing your interfaces keep in mind that an OLPC-XO in tablet mode only has the eight "keys" above available (as well as a resize-and-rotate key, but that's already mapped by the operating system).

Keep in mind that your activities will need to be localized into many languages, so binding, for instance "p" to "produce" is sub-optimal. If possible provide a run-time configuration, or at least a localization-time configuration mechanism (such as a configuration file) that lets more natural keys be chosen for each language's keyboard.

OLPC-XO (B4) Hardware Notes

The D-Pad control is usable for general control operations, but it is not a precise/fast control device as seen on gaming console controllers. It often slips from a cardinal direction to the adjacent intermediate direction (i.e. from left to left+up). You should not expect a traditional "platformer" game to be played with this control without some heuristics to clean up the input.

The checkmark button (K_KP1) is far easier to click than the X button, so "click" for "fire" should likely be the checkmark rather than the X. (Which makes sense to English users, at least). The Game pad buttons are small and close enough that asking a user to rapidly switch between them will likely result in a lot of multiple-button push events. Again, some heuristic code would be needed to clean up the input.

Cursors

See Sugar Standard Icons for instructions on how to create and use a standard Sugar cursor within Pygame-based games. The arrow and hand cursor there should likely be sufficient for most games.

Antialiased Lines

The bit-depth chosen by the wrapper (16 bit on OLPC-XOs, normally) tends to make antialiased lines fail. The reason this is so hasn't been extensively investigated, so it's not known whether this is a hard-and-fast limitation, or just an optimization hint.

Journal Integration

OLPCGames produces events to tell you about Journal save/restore requests:

  • pygame.USEREVENT
    • code = olpcgames.FILE_READ_REQUEST (OLPCGames 1.6+)
      • filename -- the filename to be read
      • metadata -- metadata object (dictionary like)
    • code = olpcgames.FILE_WRITE_REQUEST (OLPCGames 1.6+)
      • filename -- the filename to be written
      • metadata -- metadata object (dictionary like)

which are generated to allow you to save/restore to/from the Journal/Datastore on the OLPC.

Window Resizing

Window resizing doesn't work yet (i.e., resizing windows via the screen rotate button), but we will try to get this working soon.

Module Reference

The pydoc-generated documentation for the OLPCGames package serves as the canonical reference work at this point.

Customizing the Toolbar

If you want to add stuff to the standard toolbar you can override build_toolbar in your PyGameActivity subclass like this:

import pygame
import olpcgames
from sugar.graphics.toolbutton import ToolButton
from gettext import gettext as _

...

    def build_toolbar( self ):
        """Build our Activity toolbar for the Sugar system."""
        toolbar = super( MyActivityClass, self ).build_toolbar()
        
        # Add a button
        mybutton = ToolButton('activity-mybutton')  # put the icon file here: MyGame.activity/icons/activity-mybutton.svg
        mybutton.set_tooltip(_('Something'))
        mybutton.connect('clicked', self._mybutton_cb)
        toolbar.insert(mybutton, 2)
        mybutton.show()
        
        return toolbar

    def _ mybutton_cb(self, button):
        pygame.event.post(olpcgames.eventwrap.Event(pygame.USEREVENT, action='mybutton'))

Then in your event handler do this:

    if event.type == pygame.USEREVENT:
        if event.action == 'mybutton':
            self.dosomething()
        else:
            print "Unknown user event action:", event.action