As I understand it, python-config --cflags is intended to yield the C
compiler flags needed to compile a program that uses Python headers and
libraries (as opposed to the C flags needed to compile python itself).

However, it seems to include irrelevant options such as -Wall and -O3,
which interfere with the build (for example, by enabling optimisation in
a debug build):

$ python-config --cflags
-I/opt/Python-2.5.1/include/python2.5
-I/opt/Python-2.5.1/include/python2.5 -fno-strict-aliasing
-Wno-long-double -no-cpp-precomp -mno-fused-madd -DNDEBUG -g -O3 -Wall
-Wstrict-prototypes

Georg, what do you think?

I think you're right.

However, Martin, what flags except -I can/must we keep?

Some flags for the compiler are really needed to compile the Python
headers correctly, e.g. -fno-strict-aliasing in 2.6.

So I think an explicit list of options reported would have to be
maintained, either as a blacklist (e.g. -O<n>, -Wall), or as a white list.

fyi, on the mac with gcc-4.2, distutils is erroring out because of the "-
Wno-long-double" it is getting from "python-config --cflags", as it's no 
longer accepted as an argument. Fortunately this can be worked around by 
doing "CC=gcc-4.0 python setup.py".

Is this still an issue for current trunks?

It's still an issue in Python 2.6.5 as packaged by openSUSE 11.2.