python – os.getenv and os.environ don't see environment variables of my bash shell

Question

I am on ubuntu 13.04, bash, python2.7.4

The interpreter doesn’t see variables I set.

Here is an example:

$ echo $A
5
$ python -c 'import os; print os.getenv( "A" )'
None
$ python -c 'import os; print os.environ[ "A" ]'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/UserDict.py", line 23, in __getitem__
    raise KeyError(key)
KeyError: 'A'

But everything works fine with the PATH variable:

$ echo $PATH 
/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
$ python -c 'import os; print os.getenv("PATH")'
/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games

And it notices changes in PATH:

$ PATH="/home/alex/tests/:$PATH"
$ echo $PATH 
/home/alex/tests/:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
$ python -c 'import os; print os.getenv("PATH")'
/home/alex/tests/:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games

What could be wrong?

PS the problem comes when using $PYTHONPATH:

$ python -c 'import os; print os.getenv("PYTHONPATH")'
None

Asked By: xealits

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Source

Answer 1

Aha! the solution is simple!

I was setting variables with plain $ A=5 command; when you use $ export B="foo" everything is fine.

That is beca use export makes the variable available to sub-processes:

it creates a variable in the shell
and exports it into the environment of the shell
the environment is passed to sub-processes of the shell.

Plain $ A="foo" just creates variables in the shell and doesn’t do anything with the environment.

The interpreter called from the shell obtains its environment from the parent — the shell. So really the variable should be exported into the environment before.

Answered By: xealits

Answer 2

Those variables (parameters in bash terminology) are not environment variables. You want to export them into the environment, using export or declare -x. See the bash documentation on environment.

Answered By: Yann Vernier

Answer 3

Adding as I do not see an answer that has the exact issue I had. If you have multiple "shells" eg BASH and Z-Shell, ensure that you have exported the environment in the correct shell and that this is available to python.

If you are using VSCode and set the default shell to Z shell, then understandably, variables in .bashrc will not be visible to the python interpreter if they do not also exist in .zshrc. The solution then is to export the variable in both shells or change the default shell to the one with the necessary variables.

Answered By: NelsonGon

python – os.getenv and os.environ don't see environment variables of my bash shell

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