Cross-compiled Python can't find basic modules (math, operator, etc)

Question

I can't seem to import any of the basic modules located in the "lib-dynload" directory. They are all there, but I get the error: "ImportError: No module named X" when trying to import them.

I checked my sys.path and it includes the directory where all of these modules are located and my PYTHONHOME environment variable is set correctly. I'm at a bit of a loss as to what the problem could be. Some background info: This is cross-compiled from Python 2.6.6 source and installed onto an ARM embedded Linux board with Angstrom.

It did have python on there before, I had tried to bit-bake it into the image but it was missing a lot of stuff. I ended up doing my best to clean the directory tree of anything to do with the previous python before loading on my cross compiled version.

An strace of a simple script that just attempts to import math : http://pastebin.com/3XgJ3nPR

Answer 1

I see no checks in that trace for filenames like math.so or mathmodule.so which might indicate that shared-object modules are turned off entirely — that the version of Python you have compiled cannot load binary modules dynamically.

More: looking over the config.out from my most recent Python build, I see several lines where Python is investigating whether the platform will let it dynamically load binary modules that end in .so :

checking for dlopen... yes
checking DYNLOADFILE... dynload_shlib.o
checking MACHDEP_OBJS... MACHDEP_OBJS

What do these lines say on your cross-compile?

Answer 2

I have recently run across a similar issue building Python 2.7.13, and I believe it is this bug which is being fixed for Python 3 but not ported back to 2. The build process (setup.py) generates a list of modules to build, and then subtracts the list of built-in modules ( sys.builtin_module_names ); however, setup.py is run (from the Makefile) using python2.7 which in my case picked up the system (Ubuntu) binary rather than the one built, so it subtracts off modules that are built-in for the system python (including operator and collections) but not for the one being built, so they are neither built-in nor built as external modules.

I was able to use a suggestion from the bug and prepend the built python, in the source directory, to the path (and add a symlink from python2.7 -> python). This worked because I was building an x86 python on a multi-arch x64 machine; if you are building for another system like ARM you may need to apply the patch from the bug to get the list of built-in modules from earlier in the build process rather than the host python.