python extensions: including project local headers

[J Kenneth King]

Philip Semanchuk <philip at semanchuk.com> writes:

> On Oct 23, 2008, at 11:36 AM, J Kenneth King wrote:
>
>>
>> Hey everyone,
>>
>> I'm working on a python extension wrapper around Rob Hess'
>> implementation of a SIFT feature detector. I'm working on a
>> computer-vision based project that requires interfacing with Python at
>> the higher layers, so I figured the best way to handle this would be
>> in
>> C (since my initial implementation in python was ungodly and slow).
>>
>> I can get distutils to compile the extension and install it in the
>> python path, but when I go to import it I get the wonderful exception:
>>
>> ImportError: /usr/lib/python2.5/site-packages/pysift.so: undefined
>> symbol: _sift_features
>
>
> Kenneth,
> You're close but not interpreting the error quite correctly. This
> isn't an error from the compiler or preprocessor, it's a library
> error. Assuming this is dynamically linked, your OS is reporting that,
> at runtime, it can't find the library that contains _sift_features.
> Make sure that it's somewhere where your OS can find it.

This is basically what I was looking for help with. So far the project
directory is:

/pysift
  /sift
    ..
    /include
      ..
      sift.h
    /src
      ..
      sift.c
  /src
    pysift.c
  setup.py

I thought I could just #include "sift.h" in pysift.c as long as
distutils passed the right -I path to gcc.

Maybe I should compile the sift code as a shared object and link it to
my extension? How would I get distutils to build the makefile and tell
gcc how to link it?

Thanks for the reply. Python has spoiled me and my C is rather
rusty. :)