{"id":1647,"date":"2016-04-18T21:59:51","date_gmt":"2016-04-19T04:59:51","guid":{"rendered":"http:\/\/visualgdb.com\/w\/?p=1647"},"modified":"2016-04-18T21:59:51","modified_gmt":"2016-04-19T04:59:51","slug":"using-python-quick-debug-to-debug-external-python-scripts","status":"publish","type":"post","link":"https:\/\/visualgdb.com\/tutorials\/linux\/python\/quickdebug\/","title":{"rendered":"Using Python Quick Debug to debug external Python scripts"},"content":{"rendered":"

This tutorial shows how to quickly debug Python scripts and C++ modules built outside VisualGDB without creating a project for them. We will create a simple Python C++ module on a Linux machine via SSH and show how to quickly debug it with VisualGDB.<\/p>\n

Before you begin, install VisualGDB 5.1 or later.<\/p>\n

    \n
  1. First of all, connect to your Linux machine using SmarTTY and create a C++ file (e.g. test.cpp) with the following contents:\n
    #include <Python.h>\r\n#include <stdio.h>\r\n\r\nstatic PyObject *HelloMethod(PyObject *self, PyObject *args)\r\n{\r\n\u00a0\u00a0 \u00a0const char *pName = NULL;\r\n\r\n\u00a0\u00a0 \u00a0\/\/if (!PyArg_ParseTuple(args, \"s\", &pName))\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\/\/return NULL;\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0\u00a0 if (pName[0])\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0 printf(\"Hello, %s\\n\", pName);\r\n\u00a0\u00a0 \u00a0return Py_BuildValue(\"i\", 1);\r\n}\r\n\r\nstatic PyMethodDef testMethods[] = \r\n{\r\n\u00a0\u00a0 \u00a0{\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\"hello\",\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0HelloMethod,\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0METH_VARARGS,\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\"Displays a \\\"Hello\\\" message.\" \r\n\u00a0\u00a0 \u00a0},\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0{ NULL, NULL, 0, NULL }\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/* End of list *\/\r\n};\r\n\r\n\r\nPyMODINIT_FUNC inittest(void)\r\n{\r\n\u00a0\u00a0 \u00a0PyObject *m = Py_InitModule(\"test\", testMethods);\r\n\u00a0\u00a0 \u00a0if (!m)\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0return;\r\n}<\/pre>\n
    This defines a very basic Python module called “test” with a single method called “hello” that will crash the program as we commented out the actual parsing of the input arguments and are trying to dereference a NULL pointer.<\/li>\n
  2. In the same directory create a basic Python script that will call the module:\n
    import test\r\ntest.hello(\"World\")<\/pre>\n<\/li>\n
  3. Now build the module, set PYTHONPATH to point at the current directory and run the script:\n
    g++ test.cpp -ggdb -o test.so -lpython2.7 -I\/usr\/include\/python2.7 -shared\r\nexport PYTHONPATH=$PYTHONPATH:.\r\npython main.py\r\n<\/pre>\n
    Observe how the Python process crashes without printing any details:\"segfault\"<\/a><\/li>\n
  4. Now we will use Visual Studio to quickly diagnose the crash without creating any projects. Start Visual Studio and select Debug->Quick Debug with GDB:\"qdwnd\"<\/a><\/li>\n
  5. In the “Quick Debug” window select “Python Script” -> ” Linux System” and enter the following settings:\n