why can't I import the 'math' library when embedding python in c?

Question

I'm using the example in python's 2.6 docs to begin a foray into embedding some python in C. The example C-code does not allow me to execute the following 1 line script:

import math

Using line: ./tmp.exe tmp foo bar

it complains

Traceback (most recent call last):
  File "/home/rbroger1/scripts/tmp.py", line 1, in <module>
    import math
ImportError: [...]/python/2.6.2/lib/python2.6/lib-dynload/math.so: undefined symbol: PyInt_FromLong

When I do 'nm' on my generated binary (tmp.exe) it shows

0000000000420d30 T PyInt_FromLong

The function seems to be defined, so why can't the shared object find the function?

The folks at bacula seem to be in the same boat, but I don't understand why.

Answer 1

I'm using Python 2.6, and I successfully compiled and ran that same example code that you listed, without changing anything in the source.

$ gcc python.c -I/usr/include/python2.6/ /usr/lib/libpython2.6.so
$ ./a.out random randint 1 100
Result of call: 39
$ ./a.out random randint 1 100
Result of call: 57

I specifically chose the random module because it does have from math import log,... so it is certainly importing the math module as well.

Your issue is probably due to how you're linking; see this forum post for a similar issue someone else had. I can't find the links again, but it seems like there are some common issues when trying to link against Python's static library then importing modules that require a dynamic library.