[Python-Dev] Adding support to curses library

[Neal Norwitz]

On Tue, Feb 24, 2009 at 2:18 PM, Heracles
<steve at integrityintegrators.net> wrote:
>
> Hello,
>
> I am working on a patch to add to the _cursesmodule.c file of the Python
> core libraries.  I figured I would take on one of the implemented functions
> to try to get my feet wet contributing to the project.  At any rate, I have
> the following function defined in the 2.7.a version updated from SVN this
> morning:

I'm glad you are interested in developing Python.  I'm not sure if
this is the best forum.  OTOH, I'm not sure if comp.lang.python would
be appropriate either.

I'd suggest making a proper patch and submitting it to http://bugs.python.org

> ------------- Snippet ---------------------------
> // Insert new method color_set Steve Owens 2/24/2009
> //   The curses library color_set function has the following signature:
> //       int color_set(short color_pair_number, void* opts);
> static PyObject *
> PyCurses_color_set(PyObject *self, PyObject *args)
> {
>   short color_pair_number;
>   void * opts;
>   int erg;
>
>   // These macros ought to be documented in the API docs
>   // but they aren't yet.
>   PyCursesInitialised
>   PyCursesInitialisedColor
>
>   // Per ncurses Man Page:
>   //   The routine color_set sets the current color of the given window to
>   // the foreground/background combination described by the
> color_pair_number.
>   // The parameter opts is reserved for future use, applications must
> supply a
>   // null pointer.
>   switch(PyTuple_Size(args))
>   {
>   case 1:
>           // Dont make them pass a useless null pointer.
>           if (!PyArg_ParseTuple(args, "h", &color_pair_number)) return NULL;
>           break;
>   case 2:
>           // Allow them to pass the opts pointer so that when ncurses is later
> updated.
>           // This method will still work.
>           if (!PyArg_ParseTuple(args, "hO&", &color_pair_number, &opts)) return
> NULL;
>           break;
>   default:
>      PyErr_SetString(PyExc_TypeError, "color_set requires 1 or 2 arguments
> (color_pair_number[, opts]?)");
>          return NULL;
>   }
>
>   erg = color_set(color_pair_number, opts); // Debating on forcing null
> here.
>
>   if (erg == ERR)
>          return PyCursesCheckERR(erg, "color_set");
>   else
>      PyInt_FromLong((long) 1L);

I did a cursory review of the patch and if this is the exact code,
this is a problem.  You are missing a return statement.  The compiler
should have issued a warning for this too.

> }
> -------------End  Snippet ---------------------------
>
> I also have the following added in (see last line of the snippet):
>
> ------------- Snippet ---------------------------
> static PyMethodDef PyCurses_methods[] = {
>  {"baudrate",            (PyCFunction)PyCurses_baudrate, METH_NOARGS},
>  {"beep",                (PyCFunction)PyCurses_beep, METH_NOARGS},
>  {"can_change_color",    (PyCFunction)PyCurses_can_change_color,
> METH_NOARGS},
>  {"cbreak",              (PyCFunction)PyCurses_cbreak, METH_VARARGS},
>  {"color_content",       (PyCFunction)PyCurses_Color_Content,
> METH_VARARGS},
>  {"color_pair",          (PyCFunction)PyCurses_color_pair, METH_VARARGS},
>  {"color_set",           (PyCFunction)PyCurses_color_set, METH_VARARGS},
> -------------End  Snippet ---------------------------
>
> The code compiles and installs fine, but when I run the following unit test,
> I get a segmentation fault:
>
> ------------- Snippet ---------------------------
> import unittest, curses
> from test import test_support
>
> def testCursesColorSet(stdscrn):
>   curses.init_pair(1, curses.COLOR_RED, curses.COLOR_WHITE)
>   curses.init_pair(2, curses.COLOR_WHITE, curses.COLOR_BLUE);
>   i = curses.color_set(1, NULL);
>   stdscrn.addstr("RED/BLACK (%0)\n".format(i))
>   i = curses.color_set(2, NULL);
>   stdscrn.print("WHITE/BLUE (%0)\n".format(i))
>   i = curses.color_set(0, NULL);
>   stdscrn.print("Default (%0)\n".format(i))
>
>
> def test_main(stdscrn):
>   curses.savetty()
>   if curses.has_color():
>      testCursesColorSet(stdscrn)
>   else
>      stdscr.addstr( "Test Aborted: Color not supported on this terminal.")
>
>
> if __name__ == '__main__':
>    curses.wrapper(test_main)
> -------------End  Snippet ---------------------------
>
> It turns out that by commenting out this line in the _cursesmodule.c code,
> allows the unit test to run
> obviously reporting the error as expected:
>
> ------------- Snippet ---------------------------
> //erg = color_set(color_pair_number, opts); // Debating on forcing null
> here.
> -------------End  Snippet ---------------------------
>
> At any rate I am stuck.  I am still trying to build just a plain C file
> which will test the color_set function
> outside of python, but that is another task.
>
> Any suggestions?

Beyond what I said above, typically you need to go the next step.
Fire up a debugger and determine exactly where and why it's crashing.

Good luck!

n