Parsing a stdout in Python

Question

In Python I need to get the version of an external binary I need to call in my script.

Let's say that I want to use Wget in Python and I want to know its version.

I will call

os.system( "wget --version | grep Wget" )

and then I will parse the outputted string.

How to redirect the stdout of the os.command in a string in Python?

duplicate: http://stackoverflow.com/questions/89228/how-to-call-external-command-in-python — SilentGhost, Jan 20 '10 at 12:58

score 42 · Accepted Answer · edited Jan 20 '10 at 18:18

42

One "old" way is:

fin,fout=os.popen4("wget --version | grep Wget")
print fout.read()

The other modern way is to use a subprocess module:

import subprocess
cmd = subprocess.Popen('wget --version', shell=True, stdout=subprocess.PIPE)
for line in cmd.stdout:
    if "Wget" in line:
        print line

edited Jan 20 '10 at 18:18

Peter Mortensen

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answered Jan 20 '10 at 12:58

ghostdog74

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2

subprocess is new since python 2.4. – kroiz Dec 14 '15 at 21:34

score 10 · Answer 2 · answered Jan 20 '10 at 13:00

10

Use the subprocess module:

from subprocess import Popen, PIPE
p1 = Popen(["wget", "--version"], stdout=PIPE)
p2 = Popen(["grep", "Wget"], stdin=p1.stdout, stdout=PIPE)
output = p2.communicate()[0]

answered Jan 20 '10 at 13:00

Pär Wieslander

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score -2 · Answer 3 · answered Jan 20 '10 at 12:57

-2

Use subprocess instead.

answered Jan 20 '10 at 12:57

Ignacio Vazquez-Abrams

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does `Subprocess.popen` calls shell to parse command and runs an extra process in Python. – Grijesh Chauhan Dec 15 '12 at 20:35
@Grijesh: Only if you tell it to. – Ignacio Vazquez-Abrams Dec 15 '12 at 20:37
In 'C' I only use low level `pipe()` but in Python I saw people use `subproces.popen()` even there is `os.pipe()`. which practice is good? Although I can see `subprocess.popen()` is more powerful then `C` `popen()` we can explicitly send parsed command in python. – Grijesh Chauhan Dec 15 '12 at 20:48

score -3 · Answer 4 · answered Jan 20 '10 at 13:05

-3

If you are on *nix, I would recommend you to use commands module.

import commands

status, res = commands.getstatusoutput("wget --version | grep Wget")

print status # Should be zero in case of of success, otherwise would have an error code
print res # Contains stdout

answered Jan 20 '10 at 13:05

sharjeel

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bad advice: doesn't exist in py3k, docs say: Using the **`subprocess`** module is preferable to using the commands module. – SilentGhost Jan 20 '10 at 13:23

Parsing a stdout in Python

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