Set an environment variable

[Christian]

Another question from a not even newbie:

In Unix you can set an environment variable with the command
export PYTHONPATH
but I would like to set the variable from at .py script.

So my question is:
How do I export an environment variable in a .py script?
Thanks

Chris

[the_crazy88]

Just use
os.system("expo rt PYTHONPATH = %s" %("your_pythonp ath"))

[jepler]

In Unix, you generally can't affect the environment of your parent program (in
a broad sense, which includes environment variables, current working directory,
opened files, effective user ID, etc).

You have two basic choices to achieve an effect like this. First, you can
start a subshell with the desired environment, something like (untested)
os.environ['VARIABLE'] = 'value'
os.system(os.en viron['shell'])
(commands like 'su' work in this way)

Second, you can produce shell commands that have the effect of changing a
shell's environment when they are executed. Something like:
print "VARIABLE=value "
To use this, the user must write something like
eval `myscript.py`
instead of just
myscript.py
this can typically be encapsulated in a shell alias or function.
(commands like 'resize' (which sets the shell's idea of a terminal's size) work
this way)

Finally, you might be able to use an OS-specific interface like linux' ptrace
to change the actual contents of a calling process's memory. I didn't
immediately find an example of this, but on Linux it would consist of using
PTRACE_PEEKDATA and PTRACE_POKEDATA to locate the environment in another
process and modify it. The ptrace interface is not available from any standard
Python module, and isn't portable anyway. (though my manpage actually says
'CONFORMING TO SVr4, ..., X/OPEN, BSD 4.3' so maybe ptrace is more portable
than I believed)

Jeff

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[Christian]

Thanks Jeff and the crazy 88.

[Eric Brunel]

On 20 Oct 2005 01:58:44 -0700, the_crazy88 <py****@gentool inux.demon.nl> wrote:

Just use
os.system("expo rt PYTHONPATH = %s" %("your_pythonp ath"))

.... except it won't work: os.system will execute the command in a new process, so the environment variable change will only be visible in *this* process. Since you don't do anything else, the environment variable change will never be seen by anyone.

As for the OP's question, the short answer is "you can't": the Python interpreter will always be executed in a different process than the calling shell, and environment variable changes *never* impact the calling process on Unix.

The closest thing you can do is that:

-myScript.py--------------------------------------
print 'export MY_VARIABLE=val ue'
--------------------------------------------------

-myScript.sh--------------------------------------
python myScript.py > /tmp/chgvars.sh
.. /tmp/chgvars.sh
--------------------------------------------------

This is quite ugly: you write the shell commands changing the environment variables to a file, then "source" this file in the calling shell. But this is probably the best way to do what you want.

HTH
--
python -c "print ''.join([chr(154 - ord(c)) for c in 'U(17zX(%,5.zmz 5(17;8(%,5.Z65\ '*9--56l7+-'])"

[Grant Edwards]

On 2005-10-20, the_crazy88 <py****@gentool inux.demon.nl> wrote:

os.system("expo rt PYTHONPATH = %s" %("your_pythonp ath"))

No, that won't work.

That will set the environment variable in the shell spawned by
the os.system command. That shell will then immediately exit,
leaving the caller's environment unchanged.

--
Grant Edwards grante Yow! Are you mentally here
at at Pizza Hut??
visi.com

[Grant Edwards]

On 2005-10-20, Christian <ch*******@spam .not> wrote:

How do I export an environment variable in a .py script?

http://www.python.org/doc/current/li....html#l2h-1548

--
Grant Edwards grante Yow! My BIOLOGICAL ALARM
at CLOCK just went off... It
visi.com has noiseless DOZE FUNCTION
and full kitchen!!

[Mike Meyer]

"Eric Brunel" <er*********@de spammed.com> writes:

-myScript.py--------------------------------------
print 'export MY_VARIABLE=val ue'
--------------------------------------------------

-myScript.sh--------------------------------------
python myScript.py > /tmp/chgvars.sh
. /tmp/chgvars.sh

It's simpler to use eval and command substitution:

eval $(python myScript.py)

<mike

--
Mike Meyer <mw*@mired.or g> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

[Christian]

>

The closest thing you can do is that:

-myScript.py--------------------------------------
print 'export MY_VARIABLE=val ue'
--------------------------------------------------

-myScript.sh--------------------------------------
python myScript.py > /tmp/chgvars.sh
. /tmp/chgvars.sh
--------------------------------------------------

Can I write a .py script that calls a .sh script that executes the
export command and then calls another .py script (and how would the
first .py script look)?

That would be much more what is my basic problem.
Thanks

Chris

[Erik Max Francis]

Christian wrote:

Can I write a .py script that calls a .sh script that executes the
export command and then calls another .py script (and how would the
first .py script look)?

No, the shell script that the Python program would invoke would be a
different process and so commands executed in it would have no effect on
the state of another.

--
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San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Success and failure are equally disastrous.
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