Fix for get_current_track_info() when dealing with undefined values

[JohanElmis]

I was using get_current_track_info() to find the current playlist-index so I could return to the playlist after doing some announcements. Then I had an error like this:

File "/home/sonos/SoCo/soco.py", line 678, in get_current_track_info track['artist'] = metadata.findtext('.//{http://purl.org/dc/elements/1.1/}creator').encode('utf-8')

Turned out that I didn't have Artist/Title/Album defined in the ID3-tag.

Now it doesn't go down - and returns some useful info along with the playlist position. Problem solved.

[DPH]

Tested and works well - good spot. I'm new to python too so can't advise on better way to code it. Cheers David

[rahims]

Thanks, Johan!

[KennethNielsen]

Hi Johan

This is a nice catch. Thanks for fixing it up.

Even though the request is pulled I thought I would comment a bit on the "more elegant" ways part.

1) The track dictionary is already initialized to contain empty strings in line 644, which makes lines 680, 684 and 688 redundant.

2) I think the syntax if variable is a little disadvantages and it use should be minimized. As far as I remember, the metadata.findtext() function returns None if it does not find anything, so we might as well check for that directly with if variable is not None:

3) You do not need to put parentheses around the boolean statement with ifs in python.

4) In the more cosmetic department, we might do the same thing a little more compactly and without the temporary variable like so: elif d != '' and d != 'NOT_IMPLEMENTED':

Track metadata is returned in DIDL-Lite format

    metadata  = XML.fromstring(d.encode('utf-8'))
    track['title']  = metadata.findtext('.//{http://purl.org/dc/elements/1.1/}title')
    track['artist'] = metadata.findtext('.//{http://purl.org/dc/elements/1.1/}creator')
    track['album']  = metadata.findtext('.//{urn:schemas-upnp-org:metadata-1-0/upnp/}album')

    for key in ['title', 'artist', 'album']:
        if track[key] is None:
            track[key] = ''
        else:
            track[key] = track[key].encode('utf-8')

If you'd like to make any of these minor corrections, just make a separate pull request.