Malvineous Malvineous - 4 months ago 24
Python Question

How to use autotools to build Python interface at same time as library

I currently have a library written in C++, building with the GNU autotools, and I'd like to add a Python interface to it. Using SWIG I have developed the interface, but I'm having some trouble figuring out how integrate compilation of the Python module in with the rest of the process.

I have looked into AM_PATH_PYTHON but this macro doesn't seem to set the include path for Python.h, so when I compile my module I get a bunch of errors about missing include files. Is there a way to get the Python include path and ldflags out of AM_PATH_PYTHON?

Just for the record I don't think it will be possible to use Python's distutils method (setup.py) as this requires the location of the library in order to link the new module. Since the library has not yet been installed at compile time, I would have to use a relative path (e.g. ../src/lib.so) which of course would break once the Python module was installed (as the library is then in /usr/lib or /usr/local/lib instead.)

EDIT:

Now it can find the .h file it's compiling, but after installing it (in the correct location) Python can't load the module. The code produces foo.so, and when I "import foo" I get this:

ImportError: dynamic module does not define init function (initfoo)


If however I rename it from foo.so to _foo.so then it loads and runs fine, except I have to "import _foo" which I'd rather not have to do. When I follow the SWIG instructions to produce _foo.so in the current directory "import foo" works, so I am not sure why it breaks when the library is installed in the site directory.

EDIT2:

Turns out the problem was I forgot to copy foo.py produced by SWIG into the install directory alongside _foo.so. Once I did this everything worked as expected! Now I just have to figure out some automake rules to copy a file into the install dir...

Answer

To find the include path, I'd use python-config. The trick is to use the python-config corresponding to the python installed in $PYTHON.

AM_PATH_PYTHON
AC_ARG_VAR([PYTHON_INCLUDE], [Include flags for python, bypassing python-config])
AC_ARG_VAR([PYTHON_CONFIG], [Path to python-config])
AS_IF([test -z "$PYTHON_INCLUDE"], [
  AS_IF([test -z "$PYTHON_CONFIG"], [
    AC_PATH_PROGS([PYTHON_CONFIG],
                  [python$PYTHON_VERSION-config python-config],
                  [no],
                  [`dirname $PYTHON`])
    AS_IF([test "$PYTHON_CONFIG" = no], [AC_MSG_ERROR([cannot find python-config for $PYTHON.])])
  ])
  AC_MSG_CHECKING([python include flags])
  PYTHON_INCLUDE=`$PYTHON_CONFIG --includes`
  AC_MSG_RESULT([$PYTHON_INCLUDE])
])

Another alternative is to poke around in the distutils.sysconfig module (this has nothing to do with using distutils to build your code). Run python -c "import distutils.sysconfig; help(distutils.sysconfig)" and have a look.