python3: help with subprocess

[Dave Angel]

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
>   

In Python3, 'plain string' would be unicode.  But communicate returns 
bytes.  So convert them to a string, for example, by using str().  By 
default that'll assume the bytes are ASCII encoded, so if you have any 
characters above 7f, you'd need something more.

DaveA