python3: help with subprocess

[Gary Herron]

On 07/14/2010 08:38 AM, Alan wrote:
> Hi there,
>
> Module commands is gone in python3, so I am trying subprocess. So 
> please I would appreciate if someone can tell me how to do this better:
>
> before I had:
>
> cmd = 'uname -a'
> out = commands.getoutput(cmd)
>
> 'Darwin amadeus.local 10.4.0 Darwin Kernel Version 10.4.0: Fri Apr 23 
> 18:28:53 PDT 2010; root:xnu-1504.7.4~1/RELEASE_I386 i386 i386 
> MacBookPro5,2 Darwin'
>
> now:
>
> out = sub.Popen(cmd, shell=True, stderr = sub.STDOUT, stdout = 
> sub.PIPE).communicate()[0][:-1]
>
> b'Darwin amadeus.local 10.4.0 Darwin Kernel Version 10.4.0: Fri Apr 23 
> 18:28:53 PDT 2010; root:xnu-1504.7.4~1/RELEASE_I386 i386 i386 
> MacBookPro5,2 Darwin'
>
> Yes, it's ugly. the [:-1] above is to get read of the last '\n' which 
> with getoutputs I didn't have. But what's giving headache is this 
> "b'..." in the beginning.
>
> Can someone explain, point me to where I can now about it and how to 
> make this better? I wanted a plain string in out.
>
> Many thanks in advance,
>
> Alan
> -- 
> Alan Wilter S. da Silva, D.Sc. - CCPN Research Associate
> Department of Biochemistry, University of Cambridge.
> 80 Tennis Court Road, Cambridge CB2 1GA, UK.
> >>http://www.bio.cam.ac.uk/~awd28 <http://www.bio.cam.ac.uk/%7Eawd28><<


The 'b' is not part of the returned value.  If you look at the *type* of 
the returned value, you will find that it is not a string, but rather a 
byte array.   Printing of byte arrays displays the b'...' to indicate 
the type of thing begin printed.

If you want a string, then you must convert the byte array to a 
string.   For instance:

     str_out = out.decode('ascii')

(And remember:  in Python3, strings are always unicode.)

Also, using out.strip() or str_out.strip() may be a better way to remove 
the white space.

Gary Herron