Help to debug my free library

[Victor Porton]

LibComCom is a C library which passes a string as stdin of an OS command and 
stores its stdout in another string.

I wrote this library recently:
https://github.com/vporton/libcomcom

Complete docs are available at
https://vporton.github.io/libcomcom-docs/

Now I am trying to make Python bindings to the library:
https://github.com/vporton/libcomcom-python

I use CFFI (API level).

However testing my Python bindings segfaults in an unknown reason. Please 
help to debug the following:

$ LD_LIBRARY_PATH=.:/usr/local/lib:/usr/lib:/lib \
  PYTHONPATH=build/lib.linux-x86_64-2.7/ python test2.py 
Traceback (most recent call last):
Segmentation fault

(here libcomcom.so is installed in /usr/local/lib)

-- 
Victor Porton - http://portonvictor.org