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Trying to embed python into C, help!

I've been looking at using python and it's been going fairly well so far, i
can call C from python and python from C fine but now i've hit a snag and
i'm wondering how you guys have got around it.

I have to initialise python inside my C project so that i can make calls to
python modules whenever i need to but i can't create a dll for the project
as it's got to produce an exe or at least a lib so that i can execute the
initialisation code. The only way around it would seem to be to create a
separate dll project containing the python callback code that can then
import it to python and have my C code load it too. The problem with this
approach is that i'm doubtfull that the storage space for the callbacks will
be consistant between the python using the dll and C loading it. Basically
i *think* that i won't be able to get the callback data from python to C.

I know theres got to be a way around it but apart from the above i haven't
got a clue. Any help would be appreciated.

dis
Jul 18 '05 #1
2 2731
disgracelands wrote:
I've been looking at using python and it's been going fairly well so far,
i can call C from python and python from C fine but now i've hit a snag
and i'm wondering how you guys have got around it.
To be honest, I'm having some trouble understanding exactly what
your snag IS.

I have to initialise python inside my C project so that i can make calls
to python modules whenever i need to but i can't create a dll for the
project as it's got to produce an exe or at least a lib so that i can
execute the initialisation code.
....but why ever would you WANT to "create a dll" and what does THAT have
to do with "initializing Python"...?

The only way around it would seem to be to create a
separate dll project containing the python callback code that can then
import it to python and have my C code load it too. The problem with this


I'm trying to guess, from this sentence, that you labor under a
mis-apprehension that your C code, which embeds Python, can only
provide "Python extension modules" by supplying them as a separate
DLL. Is that what you mean by "the python callback code that can then
import it to python"...? Sorry if my guess is way off, but really I
find this sentence unparsable and incomprehensible.

Anyway, if that's your 'snag', rest assured that there is no such
need. Your C program can extend Python, creating modules that
Python code can import, without any DLL whatsoever. For example,
get the source distribution of Python [I don't think the demos
come with e.g. the Windows installer binary] and look at source
file Demo/embed/demo.c -- you'll see it adds to Python, as a
static module, a module 'xyzzy' from which Python code could
import and call, without arguments, a function 'foo'. Unfortunately
the Python code executed in the demo doesn't show that ability
being used, but at least you'll see 'xyzzy' listed among the
"builtin modules"; just add two lines such as:

PyRun_SimpleString("import xyzzy\n");
PyRun_SimpleString("print 'the answer is', xyzzy.foo()\n");

among the other calls to PyRun_SimpleString, and you'll see it work.
Alex
Jul 18 '05 #2
"disgracelands" <di***********@quietblue.co.uk> writes:
To be honest the entire idea of using dlls puzzled me since python
isn't platform dependant but thats the way its done in the
tutorials. The chances are that i've mis-interpreted something.


You don't have to use .dll to extend python. You can compile it
statically into the interpreter. classes such as str and dict are
compiled into the interpreter statically (as far as I know). On
platforms where some sort of dynamic linking is available such as
linux and win32, python supports linking dynamically with that
platforms dynamic link library type. That type is .dll for win32.

Clear?
--

Vennlig hilsen

Syver Enstad
Jul 18 '05 #3

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