Converting from shell to python

[Peter Otten]

Rita wrote:

> Hello,
> 
> I have been using shell for a "long" time and I decided to learn python
> recently. So far I am liking it a lot especially the argparse module which
> makes my programs more professional like.
> 
> 
> Currently, I am rewriting my bash scripts to python so I came across a
> subprocess and environment problem.
> 
> My bash script looks like this,
> 
> #!/usr/bin/env bash
> 
> export JAVA_HOME="/opt/java"
> export  PROG="dbconn"
> export JAVA_ARGS="-Xmx16g"
> export ARGS="-out outdata.dat"
> 
> $JAVA_HOME $JAVA_ARGS $PROG $ARGS
> 
> 
> To convert this into python I did something like this (which isn't working
> properly)
> 
> #!/usr/bin/env python
> import subprocess,os
> def execute():
>   try:
> 
>     cmd="$JAVA_HOME $JAVA_ARGS $PROG $ARGS"
>     cmd=cmd.split()

Here you turn cmd into a list

p=subprocess.Popen([cmd],env={"JAVA_HOME":"/opt/java","PROG":"dbconn","JAVA_ARGS":"-
Xmx16g","ARGS":"-out

and now you are wrapping it to [...], i. e. you get a list of list. Also, to 
enable shell expansion you have to invoke Popen(..., shell=True).

> outdata.dat"},
>          stdout=subprocess.PIPE)
>   except OSError, e:
>    print >>sys.stderr," Execution failed: ",e
>  return p.stdout
> 
> 
> So, I was wondering if this is the correct way of doing it? or is there an
> alternative?

I think the easiest way is to avoid environment variables and use python 
variables instead, e. g.

JAVA_HOME = "/opt/java"
JAVA_ARGS = "-Xmx16g"
#...

cmd = [JAVA_HOME, JAVA_ARGS, ...]
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)