Building things with setup.py

["Martin v. Löwis"]

James Stroud schrieb:
> I think I would like to know how to avoid or correct these sort of
> issues in the future, which seem to be limited, for me at least, to
> scipy and numpy, with the possible exception of MySQLdb and its
> dependency on zlib. Ideally, I would like to understand exactly what
> causes these errors in addition to knowing what I can do to correct them
> in the future.

Let's take a specific failure, namely the line

/auto_nfs/data10/users/jstroud/Programs/bin/g77
-L/data10/users/jstroud/Programs/lib
-L/usr/lib/gcc-lib/i386-redhat-linux/3.2.3
build/temp.linux-i686-2.5/numpy/core/blasdot/_dotblas.o
-L/data10/users/jstroud/Programs/lib -lblas -lg2c -o
build/lib.linux-i686-2.5/numpy/core/_dotblas.so

This gives errors like

build/temp.linux-i686-2.5/numpy/core/blasdot/_dotblas.o(.text+0x758):numpy/core/blasdot/_dotblas.c:226:
undefined reference to `PyTuple_New'

That's not too surprising: this line tries to link the input
*as an executable program*, despite calling the output
_dotblas.so. In an executable program, all symbols need to
be defined; that's why it it complains about so many missing
symbols (including MAIN__ - which should never be missing
in a library). Even though adding python2.5.a to the linker
link makes these symbols appear, the result still won't
work, as you can't use an executable program file as if
it were a shared library.

Now, compare this to a succeeding build of a C extension
module,

gcc -pthread -shared -L/data10/users/jstroud/Programs/lib
-L/usr/lib/gcc-lib/i386-redhat-linux/3.2.3
-I/data10/users/jstroud/Programs/include
-I/data10/users/jstroud/Programs/qt/include -I/usr/include
-I/data10/users/jstroud/Programs/include/freetype2/freetype
build/temp.linux-i686-2.5/build/src.linux-i686-2.5/numpy/core/src/umathmodule.o
-lm -o build/lib.linux-i686-2.5/numpy/core/umath.so

Notice that this passes -shared to the compiler, requesting
construction of a shared library. This is the problem with
the g77 linker line; try invoking

/auto_nfs/data10/users/jstroud/Programs/bin/g77 -shared
-L/data10/users/jstroud/Programs/lib
-L/usr/lib/gcc-lib/i386-redhat-linux/3.2.3
build/temp.linux-i686-2.5/numpy/core/blasdot/_dotblas.o
-L/data10/users/jstroud/Programs/lib -lblas -lg2c -o
build/lib.linux-i686-2.5/numpy/core/_dotblas.so

manually (whether or not -pthread is also necessary
or supported for g77, I don't know). This should at least
make the complaints about missing symbols go away; you
should then see whether the resulting module can be
imported in Python.

If that solves the problem, the question is why the
-shared option isn't passed automatically; your setting
LDFLAGS might indeed be a cause.

Regards,
Martin