how to call shell?

[Albert Hopkins]

On Tue, Feb 12, 2013, at 12:12 AM, contro opinion wrote:
> >>> import os
> >>> os.system("i=3")
> 0
> >>> os.system("echo $i")
> 
> 0
> >>>
> why i can't get the value of i ?

Whenever you call os.system, a new shell is created and the command is
run, system() then waits for the command to complete.
You don't see i because your two system() calls are in two different
processes:

python> import os
python> os.system('echo $$')
24294
0
python> os.system('echo $$')
24295
0

However, ths (e.g.) would work:

python> os.system('i=3; echo $i')
3
0

HTH,
-a