Question about envvars

[Stephen J. Turner]

Rob <rceci at my-deja.com> wrote:
> If I specify a -S, can I compensate by specifically saying at the
> appropriate time, "import site" ?

Yes you can.  In fact, older versions of Python required this; the
implicit "import site" on interpreter startup was added as of 1.5a4. 
For full information on the site module, refer to the documentation at:
  http://www.python.org/doc/current/lib/module-site.html

However, if you plan to go with this approach, consider that you
probably won't want to install your MDIreg extension module in the
$exec_prefix/lib/python1.5/site-packages directory (the usual place to
install site-wide extensions), since that directory is added to sys.path
by the site module.  You'll more likely have to put it in a custom
directory and make sure that directory in named in the PYTHONPATH
environment variable.

Even so, I'd be concerned about the fragility introduced into your
MDIreg module by this approach -- namely, that the
FileRegistry.exportEnvVars method cannot be used once the os module is
imported.  I'd much prefer to see you try the C++ subclassing suggested
below, so that your extension module works regardless of the module
import order.

Regards,
Stephen

> In article <375C3891.1D11E1A4 at ix.netcom.com>,
>   "Stephen J. Turner" <sjturner at ix.netcom.com> wrote:
>> Hi Rob,
>>
>>> 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
>>
>> Oops!  I just realized that the site module, which is imported by
>> default when the Python interpreter starts, imports the os module --
>> so by the time your script begins to execute, it's already too late.
>> Just for grins, you could try disabling the site module by adding the
>> '-S' option to the Python command line, as in:
>>
>> #!/usr/local/bin/python -S
>>
>> I'm not advocating this approach, since it's generally a good idea to
>> import the site module.  I'd just like to know if it works for you.
>>
>>> Any other ideas?  Any way to tell the os/posix module to "refresh"?
>>
>> None that I can see from looking in Modules/posixmodule.c.  Sorry.
>>
>>> 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.
>>
>> OK, how 'bout this?  Suppose you added a virtual "putenv" method to
>> your FileRegistry C++ class whose default implementation was to call
>> the global putenv function.  Then in your Python C extension, you
>> could subclass FileRegistry and override the putenv method with one
>> that modifies os.environ as described in the prior post.

--
Stephen J. Turner <sjturner at ix.netcom.com>