refactor(Track): Ensure data property is a defaultdict with dict factory

This is so both internal code and service code can save data to sub-keys without the parent keys needing to exist.

A doc-string is now set to the data property denoting some keys as reserved as well as their typing and meaning.

This also fixes a bug introduced in v3.3.3 where it will fail to download tracks without the "hls" key in the data property. This can happen when manually making Audio tracks using the HLS descriptor, and not putting any of the hls data the HLS class sets in to_tracks().

devine/core/tracks/track.py

@@ -4,6 +4,7 @@
 import re
 import shutil
 import subprocess
+from collections import defaultdict
 from copy import copy
 from enum import Enum
 from functools import partial
@@ -42,7 +43,7 @@ def __init__(
         drm: Optional[Iterable[DRM_T]] = None,
         edition: Optional[str] = None,
         downloader: Optional[Callable] = None,
-        data: Optional[dict] = None,
+        data: Optional[Union[dict, defaultdict]] = None,
         id_: Optional[str] = None,
     ) -> None:
         if not isinstance(url, (str, list)):
@@ -63,8 +64,8 @@ def __init__(
             raise TypeError(f"Expected edition to be a {str}, not {type(edition)}")
         if not isinstance(downloader, (Callable, type(None))):
             raise TypeError(f"Expected downloader to be a {Callable}, not {type(downloader)}")
-        if not isinstance(data, (dict, type(None))):
-            raise TypeError(f"Expected data to be a {dict}, not {type(data)}")
+        if not isinstance(data, (dict, defaultdict, type(None))):
+            raise TypeError(f"Expected data to be a {dict} or {defaultdict}, not {type(data)}")
 
         invalid_urls = ", ".join(set(type(x) for x in url if not isinstance(x, str)))
         if invalid_urls:
@@ -93,6 +94,7 @@ def __init__(
         self.drm = drm
         self.edition: str = edition
         self.downloader = downloader
+        self._data: defaultdict[Any, Any] = defaultdict(dict)
         self.data = data or {}
 
         if self.name is None:
@@ -132,6 +134,42 @@ def __repr__(self) -> str:
     def __eq__(self, other: Any) -> bool:
         return isinstance(other, Track) and self.id == other.id
 
+    @property
+    def data(self) -> defaultdict[Any, Any]:
+        """
+        Arbitrary track data dictionary.
+
+        A defaultdict is used with a dict as the factory for easier
+        nested saving and safer exists-checks.
+
+        Reserved keys:
+
+        - "hls" used by the HLS class.
+          - playlist: m3u8.model.Playlist - The primary track information.
+          - media: m3u8.model.Media - The audio/subtitle track information.
+          - segment_durations: list[int] - A list of each segment's duration.
+        - "dash" used by the DASH class.
+          - manifest: lxml.ElementTree - DASH MPD manifest.
+          - period: lxml.Element - The period of this track.
+          - adaptation_set: lxml.Element - The adaptation set of this track.
+          - representation: lxml.Element - The representation of this track.
+          - timescale: int - The timescale of the track's segments.
+          - segment_durations: list[int] - A list of each segment's duration.
+
+        You should not add, change, or remove any data within reserved keys.
+        You may use their data but do note that the values of them may change
+        or be removed at any point.
+        """
+        return self._data
+
+    @data.setter
+    def data(self, value: Union[dict, defaultdict]) -> None:
+        if not isinstance(value, (dict, defaultdict)):
+            raise TypeError(f"Expected data to be a {dict} or {defaultdict}, not {type(value)}")
+        if isinstance(value, dict):
+            value = defaultdict(dict, **value)
+        self._data = value
+
     def download(
         self,
         session: Session,