Lastgenre plugin crashes with canonical_tree: yes and prefer_specific: yes

[dropofwill]

Problem

When using the default canonical tree whenever a genre is unmatched _get_depth(genre) will return None, which when combined with prefer_specific will try to sort this None against a bunch of ints. For example Tycho will return this list (note (None, chillout)):

[(0, 'electronic'), (1, 'ambient'), (2, 'post-rock'), (1, 'alternative rock'), (0, 'rock'), (1, 'downtempo'), (None, 'chillout'), (2, 'shoegaze'), (2, 'idm'), (1, 'electronica')]

Traceback (most recent call last):
  File "/Users/wpaul/.asdf/installs/python/3.6.0/bin/beet", line 11, in <module>
    load_entry_point('beets==1.4.3', 'console_scripts', 'beet')()
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beets/ui/__init__.py", line 1209, in main
    _raw_main(args)
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beets/ui/__init__.py", line 1196, in _raw_main
    subcommand.func(lib, suboptions, subargs)
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 380, in lastgenre_func
    album.genre, src = self._get_genre(album)
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 322, in _get_genre
    result = self.fetch_album_genre(obj)
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 273, in fetch_album_genre
    u'album', LASTFM.get_album, obj.albumartist, obj.album
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 265, in _last_lookup
    genre = self.fetch_genre(method(*args_replaced))
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 228, in fetch_genre
    return self._resolve_genres(self._tags_for(lastfm_obj, min_weight))
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 213, in _resolve_genres
    tags = self._sort_by_depth(tags)
  File "/Users/wpaul/.asdf/installs/python/3.6.0/lib/python3.6/site-packages/beetsplug/lastgenre/__init__.py", line 178, in _sort_by_depth
    depth_tag_pairs.sort(reverse=True)
TypeError: '<' not supported between instances of 'NoneType' and 'int'

My quick fix was to call _get_depth in a guard:

depth_tag_pairs = [(self._get_depth(t), t) for t in tags if self._get_depth(t) != None]

Obviously we shouldn't be calling this twice without memoizing.

Setup

• OS: macOS Sierra
• Python version: 3.6.0
• beets version: 1.4.3

My configuration (output of beet config) is:

lastgenre:
  canonical: yes
  count: 3
  prefer_specific: yes

[sampsyo]

Thanks for the report and the diagnosis! I agree with your assessment of where the crash comes from.

Since you already have a good handle here on what's going wrong, is there any chance I can convince you to open a pull request? One simple fix, for example, would be to compute that list of pairs as-is and then add a second line that uses a second list comprehension to drop the Nones.

[ghost]

what would a 0 mean in this context?

[dropofwill]

I believe a 0 means top-level or in other words least specific genre in the the tree. None occurs whenever a genre doesn't exist in the tree.