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Example of calling IDL from Python

Atle Borsholm

This is an example of calling IDL from within Python. Python can be extended using C/C++ code, and IDL can be called from C. This requires compiling a fairly long bit of C code listed at the bottom, and for simplicity, I did this on a Linux OS (ubuntu 12.04).

The C code implements a Python module named "pidl" which consists of three methods. The methods are "getVar", "setVar" and "executeStr". This is the minimum support needed to transfer data between IDL and Python, as well as executing IDL statements and code.

The first step is to set up the shell environment so that IDL can be found from within Python. On most Linux platforms this can be done with:

export IDL_DIR=/usr/local/exelis/idl84

export LD_LIBRARY_PATH=$IDL_DIR/bin/bin.linux.x86_64



 

The next step is to create a build script for the Python module.  This is the contents of my "setup.py" file:

from distutils.core import setup, Extension

 

module1= Extension('pidl',

    include_dirs=['/usr/local/exelis/idl84/external/include'],

    libraries=['idl'],

    library_dirs=['/usr/local/exelis/idl84/bin/bin.linux.x86_64'],

    sources = ['pidl.c'])

 

setup(name= 'PackageName', version = '1.0',

    description = 'This is an IDL package', ext_modules = [module1])


 

To build and install the Python-IDL module, be sure to place the "setup.py" along with the "pidl.c" file (listed at the end), in the same directory, and execute the following command from the Linux shell (same shell as in step 1):

sudo python setup.py install


At this point the new "pidl" module should be ready to use. Here is a quick test:

$ python

Python 2.7.3 (default, Apr 10 2013, 06:20:15)

[GCC 4.6.3] on linux2

Type "help", "copyright", "credits" or "license" for more information.

>>> import pidl

IDL Version 8.4(linux x86_64 m64).(c) 2014, Exelis Visual Information Solutions, Inc.

Trial version expires on 10-feb-2015.

Licensed for use by: Exelis VIS Only

 

>>> a = [x*0.2-3.0 for x in range(31)]

>>> pidl.setVar('py_a', a)

>>> pidl.executeStr('help, py_a')

PY_A            LIST  <ID=1  NELEMENTS=31>

0

>>> pidl.executeStr('help, py_a.ToArray()')

<Expression>    DOUBLE   = Array[31]

0

>>> pidl.executeStr('b = cos(py_a.ToArray())')

0

>>> idl_b = pidl.getVar('b')

>>> idl_b

(-0.9899924966004454, -0.9422223406686581, -0.8568887533689473, -0.7373937155412454, -0.5885011172553458, -0.4161468365471424, -0.2272020946930869, -0.029199522301288593, 0.16996714290024104, 0.3623577544766736, 0.5403023058681398, 0.6967067093471655, 0.8253356149096785, 0.9210609940028851, 0.9800665778412417, 1.0, 0.9800665778412416, 0.921060994002885, 0.8253356149096782, 0.6967067093471653, 0.5403023058681398, 0.3623577544766734, 0.1699671429002406, -0.02919952230128926, -0.22720209469308775, -0.4161468365471424, -0.5885011172553458, -0.7373937155412458, -0.8568887533689475, -0.9422223406686584, -0.9899924966004454)


 

Notice that Python lists are always converted into IDL lists with this code, so the "ToArray()" method will be useful here. The IDL array is converted to a Python "tuple" by default. This C code was written few years ago for IDL 8.0, but does still seem to work when compiled with the current IDL 8.4 release.

#include <Python.h>

#include "idl_export.h"

 

typedef PyObject * PyPtr;

 

static PyPtr PidlError;

 

int AppInitIDL(void)

{

  IDL_INIT_DATA init_data;

  /* Combine any other IDL init options with NOCMDLINE */

  init_data.options = IDL_INIT_NOCMDLINE;

  return IDL_Initialize(&init_data);

}

 

static PyPtr pidl_getvar(PyPtr self, PyPtrargs)

{

  const char *varname;

  PyPtr res;

  IDL_VPTR var;

  IDL_MEMINT i;

  IDL_STRING *s;

  UCHAR *bptr;

  IDL_INT *iptr;

  IDL_LONG *lptr;

  float *fptr;

  double *dptr;

 

  if(!PyArg_ParseTuple(args, "s",&varname)) return NULL;

 

    res=Py_BuildValue("");

    var = IDL_FindNamedVariable(varname,FALSE);

    if(!var) {

    } else if (var->flags & IDL_V_ARR) {

    // array

    switch(var->type) {

    case IDL_TYP_BYTE:

      res = PyTuple_New(var->value.arr->n_elts);

      bptr = (UCHAR *) var->value.arr->data;

      for(i=0; i<var->value.arr->n_elts;i++, bptr++) {

        PyTuple_SetItem(res, i, PyInt_FromLong((long) (*bptr) ));

      }

      break;

    case IDL_TYP_INT:

      res =PyTuple_New(var->value.arr->n_elts);

      iptr = (IDL_INT *)var->value.arr->data;

      for(i=0; i<var->value.arr->n_elts;i++, iptr++) {

        PyTuple_SetItem(res, i, PyInt_FromLong((long) (*iptr) ));

      }

      break;

    case IDL_TYP_LONG:

      res = PyTuple_New(var->value.arr->n_elts);

      lptr = (IDL_LONG *)var->value.arr->data;

      for(i=0; i<var->value.arr->n_elts;i++, lptr++) {

        PyTuple_SetItem(res, i, PyInt_FromLong((long) (*lptr) ));

      }

      break;

    case IDL_TYP_FLOAT:

      res =PyTuple_New(var->value.arr->n_elts);

      fptr = (float*) var->value.arr->data;

      for(i=0; i<var->value.arr->n_elts;i++, fptr++) {

        PyTuple_SetItem(res, i,PyFloat_FromDouble( (double) (*fptr) ));

      }

      break;

    case IDL_TYP_DOUBLE:

      res =PyTuple_New(var->value.arr->n_elts);

      dptr = (double*) var->value.arr->data;

      for(i=0; i<var->value.arr->n_elts;i++, dptr++) {

        PyTuple_SetItem(res, i,PyFloat_FromDouble( *dptr ));

      }

      break;

      case IDL_TYP_STRING:

        res =PyTuple_New(var->value.arr->n_elts);

        s = (IDL_STRING *)var->value.arr->data;

        for(i=0; i<var->value.arr->n_elts;i++,s++) {

          PyTuple_SetItem(res, i,PyString_FromString( IDL_STRING_STR(s) ));

        }

        break;

      default:

        break;

      }

    } else {

    // scalar

    switch(var->type) {

    case IDL_TYP_UNDEF:

      break;

    case IDL_TYP_BYTE:

    case IDL_TYP_INT:

    case IDL_TYP_LONG:

      res=Py_BuildValue("i", IDL_LongScalar(var));

      break;

    case IDL_TYP_FLOAT:

    case IDL_TYP_DOUBLE:

      res=Py_BuildValue("f", IDL_DoubleScalar(var));

    case IDL_TYP_STRING:

      res=Py_BuildValue("s", IDL_VarGetString(var));

      break;

    case IDL_TYP_OBJREF:

      res=Py_BuildValue("s", "<IDL_OBJREF>");

      break;

    default:

      break;

    }

  }

  return res;

}

 

void py_to_idl_var(PyPtr val, int level, constchar *varname)

{

  IDL_VPTR res, tmp;

  char cmd[90], newvar[20];

  int status, i;

 

  PyPtr item;

  if(PyList_Check(val)) {

    sprintf(cmd, "%s = obj_new('list')", varname);

    status = IDL_ExecuteStr(cmd);

    sprintf(newvar, "_$tmp%6.6d",level);

    for (i=0; i<PyList_Size(val); i++) {

      py_to_idl_var( PyList_GetItem(val, i),level+1, newvar );

     sprintf(cmd, "%s->Add, temporary(%s)",varname, newvar);

      status = IDL_ExecuteStr(cmd);

    }

  } else if (PyInt_Check(val)) {

    tmp = IDL_GettmpLong64( PyInt_AsLong(val));

    res = IDL_FindNamedVariable(varname, TRUE);

    IDL_VarCopy(tmp, res);

  } else if (PyFloat_Check(val)) {

    tmp = IDL_GettmpDouble(PyFloat_AsDouble(val) );

    res = IDL_FindNamedVariable(varname, TRUE);

    IDL_VarCopy(tmp, res);

  } else if (PyString_Check(val)) {

    tmp = IDL_StrToSTRING(PyString_AsString(val) );

    res = IDL_FindNamedVariable(varname, TRUE);

    IDL_VarCopy(tmp, res);

  } else {

    tmp = IDL_GettmpLong( -1 );

    res = IDL_FindNamedVariable(varname, TRUE);

    IDL_VarCopy(tmp, res);

  }

}

static PyPtr pidl_setvar(PyPtr self, PyPtrargs)

{

  const char *varname;

  PyPtr val;

  IDL_VPTR idlvar, prev;

 

  if(!PyArg_ParseTuple(args, "sO",&varname, &val)) return NULL;

  py_to_idl_var(val, 0,varname);

  return Py_BuildValue("");

}

 

static PyPtr pidl_exec(PyPtr self, PyPtr args)

{

  const char *command;

  int sts;

 

  if(!PyArg_ParseTuple(args, "s",&command)) return NULL;

  sts = IDL_ExecuteStr(command);

  return Py_BuildValue("i", sts);

}

 

static PyMethodDef PidlMethods[] = {

  {"executeStr",pidl_exec, METH_VARARGS, "Execute an IDLcommand."},

  {"getVar",pidl_getvar, METH_VARARGS, "Get an IDLvariable."},

  {"setVar",pidl_setvar, METH_VARARGS, "Set an IDLvariable."},

  {NULL},

};

 

PyMODINIT_FUNC initpidl(void)

{

  PyPtr m;

  m = Py_InitModule("pidl",PidlMethods);

  if (m == NULL) return;

 

  if(!AppInitIDL()) return;

 

  PidlError = PyErr_NewException("pidl.error", NULL,NULL);

  Py_INCREF(PidlError);

  PyModule_AddObject(m, "error", PidlError);

}

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