Python and regex

Question

i have to parse need string. Here is command I execute in Linux console:

amixer get Master |grep Mono:

And get, for example,

Mono: Playback 61 [95%] [-3.00dB] [on]

Then i test it from python-console:

import re,os
print re.search( ur"(?<=\[)[0-9]{1,3}", u"  Mono: Playback 61 [95%] [-3.00dB] [on]" ).group()[0]

And get result: 95. It's that, what i need. But if I'll change my script to this:

print re.search( ur"(?<=\[)[0-9]{1,3}", str(os.system("amixer get Master |grep Mono:")) ).group()[0]

It'll returns None-object. Why?

SilentGhost · Accepted Answer · 2009-08-14 17:29:24Z

7

os.system() returns the exit code from the application, not the text output of the application.

You should read up on the subprocess Python module; it will do what you need.

edited Aug 14, 2009 at 17:29

SilentGhost

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answered Aug 14, 2009 at 17:26

retracile

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2 Comments

Max Frai Over a year ago

If i do: temp = os.system("amixer get Master |grep Mono:") & print temp i get output result. Or i'm wrong?

retracile Over a year ago

The output from the command is going to stdout directly, and not to the 'temp' variable. Try running that test with 'print "the value of temp is %s characters long, and is: %s" % (len(temp), temp)

John Millikin · Accepted Answer · 2009-08-14 17:30:24Z

1

Instead of using os.system(), use the subprocess module:

from subprocess import Popen, PIPE
p = Popen("amixer get Master | grep Mono:", shell = True, stdout = PIPE)
stdout = p.stdout.read()
print re.search( ur"(?<=\[)[0-9]{1,3}", stdout).group()

answered Aug 14, 2009 at 17:30

John Millikin

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Comments

Stefan Kendall · Accepted Answer · 2009-08-14 17:28:02Z

0

How to run a process and get the output:

http://docs.python.org/library/popen2.html

answered Aug 14, 2009 at 17:28

Stefan Kendall

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2 Comments

SilentGhost Over a year ago

Deprecated since version 2.6: This module is obsolete. Use the subprocess module.

Stefan Kendall Over a year ago

Which is linked to in that documentation, but I found popen to be more clear. Thanks for the downvote, though.

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