* Readability and consistency
* Better logging: warn by default for attributes that were not found,
but don't drown user with info when everything is going well.
* I don't see DefaultList be really helpful in many other cases, so having
a beets.util.collections module (which could also conflict with the collections
module from standard library) with only that in it is a little silly.
* It was elegant and concise, but there are implementation issues: it is not
recommended to subclass builtin types, but the alternatives differ between python
2 and 3 (subclass sequence or container or collections.abc?), moreover,
interpreters can differ in the way they map syntaxic sugar to magic functions.
* Also, slicing and negative indexing could do weird things, so the class wouldn't
be really intuitive and simple at the same time
Fixes#587. The disc field is only zero when there is only one medium, so I think this will do the trick. I wasn't able to reproduce the real problem within the code. This is just a small workaround.
Modify coalesce_tracks() in order to handle the case where subtracks
are defined inside an index track (as `sub_tracks` attribute),
reorganizing the if logic to avoid duplicated code.
Add a try..catch block enclosing the call to clean_tracklist, as a
measure for avoiding side effects (and reverting to just parsing the
raw_list if there are any problems).
Revise the regular expression used for extracting information from a
discogs position, making the subtrack_index only be matched if one of
the other groups is matched as well. Split the definition into several
lines in order to try to document it a bit more clearly.
Add unit tests for position parsing and non standard positions.
Fix the underscore on tox dependency.
Detect subtracks and merge them into a single track, taking into account
the index tracks if present. This includes a revision of the regular
expression used for converting a discogs "position" into medium, medium
index and subtrack index pieces, following the standard discogs
positions (12.2.9).
Rather than using an unordered set for storing pairs, append to a list
and build an OrderedDict from it to filter duplicated strings while
keeping order.
Fallout from #2188. Following @jrobeson's suggestion, I just turned the check
in LibModel.__format__ into an assert. This turned up a few badly-behaved
clients, which are also fixed.
