Question about envvars

[rceci at my-deja.com]

Stephen,

Boy I was excited to get a reasonable explaination so quickly, but alas,
it still does not work.  Here is my test script:

#!/usr/local/bin/python

import MDIreg

reg = MDIreg.FileRegistry(1,1)
reg.exportEnvVars()

import os
print "child has it : "
os.system("env | grep MDI_REG_VERSION")
print "but do I have it? :"
print os.environ['MDI_REG_VERSION']

---

I am interested in this "MDI_REG_VERSION" envvar which gets exported by
my library.  Here is the output:

child has it :
MDI_REG_VERSION=10.0
but do I have it? :
Traceback (innermost last):
  File "regtest.py", line 12, in ?
    print os.environ['MDI_REG_VERSION']
  File "/usr/local/lib/python1.5/UserDict.py", line 12, in __getitem__
    def __getitem__(self, key): return self.data[key]
KeyError: MDI_REG_VERSION

Any other ideas?  Any way to tell the os/posix module to "refresh"?

By the way, thanks for the library implementation suggestion, but I must
keep it the way it is, because other c, and c++ (at the class level)
programs access this library.

Thanks

Rob



In article <375BFE38.3FB3E83C at ix.netcom.com>,
  "Stephen J. Turner" <sjturner at ix.netcom.com> wrote:
> Hi Rob,
>
> > I have built a shared module that reads flat files for environment
> > variable information, and makes subsequent putenv calls for those
> > pertinent ones.  This functionality is encapsulated in a c++ class,
> > FileRegistry, which I think I have working correctly, using shadow
> > classes under python.  All I expose in the class is the ctor, the
dtor,
> > and the method called exportEnvVars():
> >
> > %module MDIreg
> > %{
> > #include "fileregistry.h"
> > %}
> >
> > class FileRegistry
> > {
> > public:
> >   FileRegistry(bool, bool);
> >  ~FileRegistry();
> >   void exportEnvVars();
> > };
> >
> > ...
> >
> > However, I can't seem to get the envvars to persist into the current
> > process space.  If I fork off a child, then I can see the envvars
that I
> > expect.
>
> The problem is that, although putenv does indeed modify the current
> process's environment, Python only reads the environment when the
posix
> module (imported by os) is first imported, so as to create the environ
> dictionary.  (Try confirming this behavior by postponing "import os"
> until after your call to MDIreg.exportEnvVars.  You should see your
> environment changes reflected in os.environ.)
>
> The proper solution is, I think, to avoid the direct use of the putenv
> function, and instead to use the Python C API to modify the os.environ
> mapping (which calls putenv as a side effect).  Here is a crude C
module
> to do just such a thing:
>
> -------------------- START modenv.c --------------------
> #include <Python.h>
>
> #include <stdio.h>
> #include <string.h>
>
> static PyObject *modenv_load(PyObject *self, PyObject *args)
> {
>   FILE *fp;
>   PyObject *os, *environ, *v;
>   char buf[256];
>   char *file;
>   char *value;
>
>   if (!PyArg_ParseTuple(args, "s", &file))
>     return NULL;
>
>   os = PyImport_ImportModule("os");
>   environ = PyObject_GetAttrString(os, "environ");
>
>   if (fp = fopen(file, "r")) {
>     while (fgets(buf, sizeof(buf), fp), !feof(fp)) {
>       /* skip lines that do not contain equals sign */
>       if (!(value = strchr(buf, '=')))
> 	continue;
>
>       /* remove trailing newline */
>       buf[strlen(buf)-1] = '\0';
>
>       *value++ = '\0';
>       v = PyString_FromString(value);
>       PyMapping_SetItemString(environ, buf, v);
>       Py_DECREF(v);
>     }
>     fclose(fp);
>   }
>
>   Py_DECREF(environ);
>   Py_DECREF(os);
>
>   Py_INCREF(Py_None);
>   return Py_None;
> }
>
> static struct PyMethodDef modenv_methods[] = {
>   {"load", (PyCFunction)modenv_load, METH_VARARGS},
>   {NULL, (PyCFunction)NULL, 0, NULL}
> };
>
> void initmodenv()
> {
>   if (!Py_InitModule4("modenv", modenv_methods, NULL, NULL,
> 		      PYTHON_API_VERSION))
>     Py_FatalError("can't initialize module modenv");
> }
> -------------------- END modenv.c --------------------
>
> Hope it helps.
>
> Regards,
> Stephen
>
> --
> Stephen J. Turner <sjturner at ix.netcom.com>
>


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