Segmentation fault in Python 3 PyType_Ready

Question

I have an application that starts in C++ and calls into Python that I'm converting to Python 3. I'm getting a segmentation fault in PyType_Ready that I do not get on python 2.

Here are the steps to reproduce on CENTOS 7, gcc 4.8.5, using conda to get py2/py3:

cd $WORKING # new empty directory
wget https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh
bash Miniconda3-latest-Linux-x86_64.sh # use $WORKING/mc3 for the prefix
source mc3/etc/profile.d/conda.sh
conda create -n py2 python=2
conda create -n py3 python=3
conda activate py2
export LD_LIBRARY_PATH=$CONDA_PREFIX/lib
g++ -o dummy_py2 -I$CONDA_PREFIX/include/python2.7 -L$CONDA_PREFIX/lib -lpython2.7 dummy.cpp
./dummy_py2 # this runs ok
conda deactivate
conda activate py3
export LD_LIBRARY_PATH=$CONDA_PREFIX/lib
g++ -o dummy_py3 -I$CONDA_PREFIX/include/python3.8 -L$CONDA_PREFIX/lib -lpython3.8 dummy.cpp
./dummy_py3 # seg fault

Where dummy.cpp is:

#define PY_SSIZE_T_CLEAN
#include "Python.h"

typedef struct {
    PyObject_HEAD
    const char *data;
} MyObject;

static PyTypeObject MyObject_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "mymod.MyObject",               /* tp_name */
    sizeof(MyObject),               /* tp_basicsize */
    0,                              /* tp_itemsize */
};


int main() {
  printf("This is a dummy test\n");
  PyType_Ready(&MyObject_Type);
  printf("We did it\n");
  return 0;
}

I've used gdb to get the stack trace (edited for paths):

#0  0x00007f6966929b62 in PyTuple_New () from $CONDA_PREFIX/lib/libpython3.8.so.1.0
#1  0x00007f696692bb46 in PyType_Ready () from $CONDA_PREFIX/lib/libpython3.8.so.1.0
#2  0x00007f696692ca27 in PyType_Ready () from $CONDA_PREFIX/lib/libpython3.8.so.1.0
#3  0x00000000004006b5 in main ()

Relevant reference (I'm using the Examples section): https://docs.python.org/3/c-api/typeobj.html

I've tried to create this minimal example from a much bigger application but hopefully this is a supported use case? Thanks for any help.

Aaron S. Brewster · Accepted Answer · 2020-01-13 22:57:28Z

1

Ok, solved it. I needed to add Py_Initialize. New code that works:

int main() {
  printf("This is a dummy test\n");
  Py_Initialize();
  PyType_Ready(&MyObject_Type);
  printf("We did it\n");
  return 0;
}

answered Jan 13, 2020 at 22:57

Aaron S. Brewster

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