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PlaylistFilters

When creating playlists, the playlist_builder calls filter_tag_playlists with a configurable list of PlaylistFilter implementations:

Source code in src/djtools/collection/helpers.py 
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def filter_tag_playlists(
    playlist: Playlist, playlist_filters: List[PlaylistFilter]
) -> None:
    """Applies a list of PlaylistFilter implementations to the playlist.

    If the PlaylistFilter implementations' is_filter_playlist method evaluates
    to True, then the filter_track method is applied to each track in the
    playlist. The playlist's tracks are set to remove the tracks that have been
    filtered out.

    Args:
        playlist: Playlist to potentially have its tracks filtered.
        playlist_filters: A list of PlaylistFilter implementations used to
            filter playlist tracks.
    """
    # This is a folder so filter its playlists.
    if playlist.is_folder():
        for _playlist in playlist:
            filter_tag_playlists(_playlist, playlist_filters)
        return

    # Apply each PlaylistFilter to this playlist.
    for playlist_filter in playlist_filters:
        if not playlist_filter.is_filter_playlist(playlist):
            continue
        playlist.set_tracks(
            tracks={
                track_id: track
                for track_id, track in playlist.get_tracks().items()
                if playlist_filter.filter_track(track)
            },
        )

These PlaylistFilters inject custom behavior into the playlist_builder. In general, this is done by scanning through a playlist structure and looking for a playlist, or playlists, that match some description and then filter for tracks that match another description.

Source code in src/djtools/collection/playlist_filters.py 
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class PlaylistFilter(ABC):
    "This class defines an interface for filtering tracks from playlists."

    @abstractmethod
    def filter_track(self, track: Track) -> bool:
        """Returns True if this track should remain in the playlist.

        Args:
            track: Track object to apply filter to.

        Returns:
            Whether or not this track should be included in the playlist.
        """

    @abstractmethod
    def is_filter_playlist(self, playlist: Playlist) -> bool:
        """Returns True if this playlist should be filtered.

        Args:
            playlist: Playlist object to potentially filter.

        Returns:
            Whether or not to filter this playlist.
        """

PlaylistFilter subclasses must implement two methods:

  • is_filter_playlist: returns True if a given Playlist should have the filter applied to its tracks
  • filter_track: returns True if a track should remain in the playlist after applying the filter.

Once a PlaylistFilter is implemented, it must be added to the list of supported COLLECTION_PLAYLIST_FILTERS:

Source code in src/djtools/collection/config.py 
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class CollectionConfig(BaseConfig):
    """Configuration object for the collection package."""

    COLLECTION_PATH: Optional[Path] = None
    COLLECTION_PLAYLIST_FILTERS: List[
        Literal[
            "HipHopFilter",
            "MinimalDeepTechFilter",
            "ComplexTrackFilter",
            "TransitionTrackFilter",
        ]
    ] = []
    COLLECTION_PLAYLISTS: bool = False
    COLLECTION_PLAYLISTS_REMAINDER: Literal["folder", "playlist"] = "folder"
    COPY_PLAYLISTS: List[str] = []
    COPY_PLAYLISTS_DESTINATION: Optional[Path] = None
    PLATFORM: Literal["rekordbox"] = "rekordbox"
    SHUFFLE_PLAYLISTS: List[str] = []
    playlist_config: Optional[PlaylistConfig] = None

    def __init__(self, *args, **kwargs):
        """Constructor.

        Raises:
            RuntimeError: Using the collection package requires a valid
                COLLECTION_PATH.
            RuntimeError: Failed to render collection_playlist.yaml from
                template.
            RuntimeError: COLLECTION_PATH must be a valid collection path.
            RuntimeError: collection_playlists.yaml must be a valid YAML file.
        """
        super().__init__(*args, **kwargs)

        if any(
            [
                self.COLLECTION_PLAYLISTS,
                self.COPY_PLAYLISTS,
                self.SHUFFLE_PLAYLISTS,
            ]
        ) and (not self.COLLECTION_PATH or not self.COLLECTION_PATH.exists()):
            raise RuntimeError(
                "Using the collection package requires the config option "
                "COLLECTION_PATH to be a valid collection path"
            )

        if self.COLLECTION_PLAYLISTS:
            config_path = Path(__file__).parent.parent / "configs"
            env = Environment(
                loader=FileSystemLoader(config_path / "playlist_templates")
            )
            playlist_template = None
            playlist_template_name = "collection_playlists.j2"
            playlist_config_path = config_path / "collection_playlists.yaml"

            try:
                playlist_template = env.get_template(playlist_template_name)
            except TemplateNotFound:
                pass

            if playlist_template:
                try:
                    playlist_config = playlist_template.render()
                except Exception as exc:
                    raise RuntimeError(
                        f"Failed to render {playlist_template_name}: {exc}"
                    ) from exc

                if playlist_config_path.exists():
                    logger.warning(
                        f"Both {playlist_template_name} and "
                        f"{playlist_config_path.name} exist. Overwriting "
                        f"{playlist_config_path.name} with the rendered "
                        "template"
                    )

                with open(
                    playlist_config_path, mode="w", encoding="utf-8"
                ) as _file:
                    _file.write(playlist_config)

            if not playlist_config_path.exists():
                raise RuntimeError(
                    "collection_playlists.yaml must exist to use the "
                    "COLLECTION_PLAYLISTS feature"
                )

            try:
                with open(
                    playlist_config_path, mode="r", encoding="utf-8"
                ) as _file:
                    self.playlist_config = PlaylistConfig(
                        **yaml.load(_file, Loader=yaml.FullLoader) or {}
                    )
            except ValidationError as exc:
                raise RuntimeError(
                    "collection_playlists.yaml must be a valid YAML to use "
                    "the COLLECTION_PLAYLISTS feature"
                ) from exc

PlaylistFilter Implementations

The playlist_filters module contains the following set of PlaylistFilter implementations: - HipHopFilter - MinimalDeepTechFilter - TransitionTrackFilter - ComplexTrackFilter

HipHopFilter

  • Checks to see if a playlist named 'Hip Hop' is a child of a playlist named 'Bass'
  • If it is, then tracks in that playlist must have a genre tag besides 'Hip Hop' and 'R&B'
  • If it is not, then tracks in that playlist must have only genre tags 'Hip Hop' and 'R&B'

MinimalDeepTechFilter

  • Checks to see if a playlist named 'Minimal Deep Tech' is a child of a playlist named 'Techno' or 'House'
  • If it's a child of a 'Techno' playlist, then at least one other genre tag must contain the substring 'techno' (case insensitive)
  • If it's a child of a 'House' playlist, then at least one other genre tag must contain the substring 'house'

ComplexTrackFilter

  • Checks to see if the playlist, or a parent playlist, contains the substring 'complex'
  • Filters tracks that contain fewer than a set number of tags (only includes "other" tags, does not include genre tags)
  • When instantiated, ComplexTrackFilter takes optional arguments for the minimum_tags_for_complex_track as well as the list of exclude_tags which may not count towards the total number of tags

TransitionTrackFilter

  • Checks to see if the playlist, or a parent playlist, contains the substring 'transition'
  • Checks to see if the playlist contains one, and only one, of the substrings 'genre' or 'tempo'
  • Filters tracks that contain a special annotation in their comments field
  • The expected annotation must match the following syntax [ token1 / token2] where a token must be strings if it's a 'genre' transition playlist or numbers if it's a 'tempo' transition playlist