[python-win32] regarding invoking command prompt using python

[Vernon Cole]

Tim:
  Okay, explain this...
C:\BZR\sterling\HL7>c:\python26\python.exe
Python 2.6.2 (r262:71605, Apr 14 2009, 22:40:02) [MSC v.1500 32 bit (Intel)]
on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.putenv('x','test')
>>> print os.getenv('x')
zzz
>>> exit()

C:\BZR\sterling\HL7>set x
x=zzz

C:\BZR\sterling\HL7>
--
Vernon


On Wed, Jun 17, 2009 at 8:11 PM, Tim Roberts <timr at probo.com> wrote:

> Vernon Cole wrote:
> >
> > Similarly, it seems that getenv() and putenv() should be inverse
> > functions, but they are not. os.getenv() refers to the parent
> > environment, os.putenv() refers to the child environment.
>
> No, no, no!  That's not true at all!  BOTH of those functions refer to
> the environment of the CURRENT PROCESS.  I inherited my environment from
> my parent process (which is often a shell).  I can change my environment
> as much as I wish.  When I create new processes, those processes inherit
> my current environment, with whatever changes I made.  I can't change my
> parent's environment, and I can't change my children's environment.  I
> can only hand off a copy of my environment to my children, which they
> are free to modify themselves.
>
>
> > We have established that there is no (documented) inverse function for
> > getenv() -- although shells do it somehow.
>
> We have not established that at all!  getenv() gets from the current
> process environment, and putenv() modifies the current process
> environment.  When you type a "set" command in a command shell, that
> executes inside bash (or cmd.exe or sh or whatever).  In handling "set",
> bash calls putenv, which modifies bash's environment.  Bash can see that
> change, of course, and any future processes that bash spawns will
> include those changes.
>
>
> > Is there an inverse for putenv() so that I can see what my children
> > will see?
>
> Of course you can!  If YOU call putenv(), then YOU can call getenv() and
> see the changes you made to your environment.  However, when you exit,
> all of your changes evaporate with your process.  The parent process,
> whatever it is, continues to exist with the environment it had before.
>
> --
> Tim Roberts, timr at probo.com
> Providenza & Boekelheide, Inc.
>
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