beginner questions on embedding/extending python with C++

[Qun Cao]

Hi Everyone,

I am a beginner on cross language development. My problem at hand is to
build a python interface for a C++ application built on top of a 3D
game engine. The purpose of this python interface is providing a
convenient scripting toolkit for the application. One example is that
a user can write a python script like:
player = Player()
game.loadPlayer(player)
player.moveTo(location)
To configure the game environment.

I am trying to figure out how to make this happen. I only have the
vague idea that this concerns embedding/extending python with C++, but
after reading Python Doc, SWIG, BOOST.Python, I am still not sure how
to architecture it.

Since the main program is still going to be the C++ application, I
guess we need to embedding the python scripts in the C++ code. So at
initialization stage, the python script needs to be loaded into the C++
code. And this code can be simple, like
player = Player()
game.loadPlayer(player)


But for this to work, the python code needs to know the Player class,
is it right? Does that mean I need to build a python wrapper class for
Player and "import Player" in the python code? But because this
application is built on top of a game engine, Player class inherits
many classes from there, I cannot possibly wrapping them all, right?
Also, some global objects are probably needed in this code of adding
players, how can the python code access them?

I know I probably don't have a grasp of basics here, please kindly
enlighten me!

Btw, if you can point me to any source code of non-trivial projects
utilizing SWIG/Boost.Python, that would be very helpful. I found the
examples on the tutorials are far too simple.

Thank you very much,
Qun

 

[Diez B. Roggisch]

Since the main program is still going to be the C++ application, I

guess we need to embedding the python scripts in the C++ code. So at
initialization stage, the python script needs to be loaded into the C++
code. And this code can be simple, like
player = Player()
game.loadPlayer(player)


But for this to work, the python code needs to know the Player class,
is it right? Does that mean I need to build a python wrapper class for
Player and "import Player" in the python code? But because this
application is built on top of a game engine, Player class inherits
many classes from there, I cannot possibly wrapping them all, right?
Also, some global objects are probably needed in this code of adding
players, how can the python code access them?

You should look into SIP besides the tools you already mentioned - IMHO it
is the best choice for wrapping C++.

And yes, you need to wrap classes - but only those that are of interest for
you! So if you need Player, wrap Player. No need to wrap it's base-classes,
unless you want these for other purposes, too.

And for global objects I'd create functions which return these.

I suggest you try and download a project that uses one of the possible
toolkits for wrapping - the most prominent user of SIP is of course PyQt.
Go and have a look at the source, how things are done. There aresome
tutorials I think, google should help you on that.

HTH Diez

 

[Roman Yakovenko]

Hi Everyone,

I am a beginner on cross language development. My problem at hand is to
build a python interface for a C++ application built on top of a 3D
game engine. The purpose of this python interface is providing a
convenient scripting toolkit for the application.

As for me, Boost.Python is the way to go.

Fortunately you are not the first one, and I hope not the last one :

http://language-binding.net/pyplusplus/quotes.html#who-is-using-pyplusplus
1. Python-OGRE
* http://lakin.weckers.net/index_ogre_python.html
* http://tinyurl.com/mvj8d

2. http://cgkit.sourceforge.net/ - contains Python bindings for Maya C++ SDK

3. PyOpenSG - https://realityforge.vrsource.org/view/PyOpenSG/WebHome
The goal of PyOpenSG is to provide python bindings for the OpenSG
scene graph.

Since the main program is still going to be the C++ application, I
guess we need to embedding the python scripts in the C++ code.

Boost.Python is the only tool that provides complete functionality(
extending and
embedding ). Also I think cgkit is dealing with the problem too.

But for this to work, the python code needs to know the Player class,
is it right?

Right.

Does that mean I need to build a python wrapper class for

Player and "import Player" in the python code? But because this
application is built on top of a game engine, Player class inherits
many classes from there, I cannot possibly wrapping them all, right?

It depends on how much functionality you want to export.

Also, some global objects are probably needed in this code of adding
players, how can the python code access them?

Boost.Python provides the functionality you need.

Btw, if you can point me to any source code of non-trivial projects
utilizing SWIG/Boost.Python, that would be very helpful. I found the
examples on the tutorials are far too simple.

Those are tutorials, they should be simple, right ?

 

[Ben Sizer]

Hi Everyone,

I am a beginner on cross language development. My problem at hand is to
build a python interface for a C++ application built on top of a 3D
game engine. The purpose of this python interface is providing a
convenient scripting toolkit for the application.

As well as this group/list, you may find some useful help at the
Gamedev.net Scripting Languages and Game Modifications forum:
http://www.gamedev.net/community/forums/forum.asp?forum_id=41

Many people there have mixed Python and C++ code in the context of game
applications and may have some good answers to your questions. After
deciding how to expose C++ classes and functions to Python, the main
problem you'll face, assuming you need the functionality, is how to
yield control between Python and C++ when a Python action is
long-running yet requires the C++ engine to be polled (eg. to handle
input, AI, graphics, etc). Previous threads there will give you some
hints on all these matters.

 

[Qun Cao]

Thanks Diez,
It is a good relief that I only need to wrap the classes I need. I
decide to try Boost first because it seems to have a wider audience
than SIP, but I would definately look into SIP if I want to do Qt
development in the future.

 

[Qun Cao]

Thanks for all the good pointers!
I am still reading throught them, but Boost seems to be the way to go!

 

[Hoop]

Hi All,
I am in the process also of trying to call Python script from a C++
windows app.
I have looked at the Boost site and am currently reading over the
Embedding portion of the tutorial. A question I have is that there
appear to be about 4 or 5 Boost items avaiable for download. Which one
should be downloaded to do the embedding?
Thanks
Jeff