Is there an extension library?
Martin v. Löwis
martin at v.loewis.de
Sat Sep 27 08:20:39 CEST 2003
"Letbetter, Jason" <letbetter at ti.com> writes:
> I'm creating Python extensions for several c/c++ components. I'm using
> swig to create the extensions. The biggest challenge so far is working with
> the c args between Python and the Python extension. Is there a 3rd party
> library of extension helpers that assist in representing c-types between
> Python and c? Are there any tips and tricks?
I suggest not to use swig, or any tools - atleast not until you fully
understand how to use these tools (I, for one, don't know how to use
swig, so I don't use it).
> 1) Refrencing and derefrencing:
> For example, condsider this c api:
> void foo_alloc(void** handle_ptr);
> void foo_use(void* handle);
> In c &handle. How to get pointer to pointer in Python?
> In c *handle_ptr. How to derefrence a pointer in Python?
I recommend to wrap this in a Python object type:
Then, in PyFoo_New, invoke foo_alloc, and implement a method PyFoo_use
of the PyFoo objects.
> "TypeError: CharArray___setitem__() argument 3 must be char, not int"
> In c, buf[i] = (char)i, is implicit. How do I do it in Python. Why doesn't
> Python make this conversion implicitly?
Because in Python, characters are *not* numbers (unlike in C). In
Python, characters are strings of length 1.
Again, if you want to store chars in setitem: don't use swig, but
write it yourself.
> 3) It seems like I'm doing something unatural with my Python extension. It
> seems someone else may have already figured out the best way to transform c
> arguments between Python and Python extensions genericly.
The best way to transform a C library into a Python extension is to
write the extension module by hand.
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