NEWBIE: Tokenize command output

Tim Chase python.list at tim.thechases.com
Thu May 11 17:45:17 CEST 2006


Lorenzo Thurman wrote:
> This is what I have so far:
> 
> //
> #!/usr/bin/python
> 
> import os
> 
> cmd = 'ntpq -p'
> 
> output = os.popen(cmd).read()
> //
> 
> The output is saved in the variable 'output'. What I need to do next is 
> select the line from that output that starts with the '*'

Well, if you don't need "output" for anything else, you can 
just iterate over the lines with

import os
cmd = 'ntpq -p'
p = os.popen(cmd)
starLines = [line for line in p.readlines() if 
line.startswith("*")]

or you may optionally want to prune of the "\n" characters 
in the process:

starLines = [line[:-1] for line in p.readlines() if 
line.startswith("*")]

If there's only ever one, then you can just use

myLine = starLines[0]

Otherwise, you'll have to react accordingly if there are 
zero lines or more than one line that begin(s) with an asterisk.

>      remote           refid      st t when poll reach   delay   offset  
> jitter
[cut]

> *caesar.cs.wisc. 128.105.201.11   2 u  635 1024  377   29.514   -0.231   
> 0.077
> 
>>From there, I need to tokenize the line using the spaces as delimiters. 
> Can someone give me some pointers?

Again, you can use the one-line pythonizm of "tuple 
unpacking" here (the split() method takes an optional 
parameter for the delimiter, but defaults to whitespace):

remote, refid, st, t, when, poll, reach, delay, offset, 
jitter = myLine.split()

If you just want one of them, you can do it by offset:

	delay = myLine.split()[7]

HTH,

-tkc









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