Make LazyClassProperty / cached_classproperty reusable

beets/autotag/hooks.py

@@ -39,7 +39,7 @@ from unidecode import unidecode
 from beets import config, logging, plugins
 from beets.autotag import mb
 from beets.library import Item
-from beets.util import as_string
+from beets.util import as_string, cached_classproperty
 
 log = logging.getLogger("beets")
 
@@ -413,23 +413,6 @@ def string_dist(str1: Optional[str], str2: Optional[str]) -> float:
     return base_dist + penalty
 
 
-class LazyClassProperty:
-    """A decorator implementing a read-only property that is *lazy* in
-    the sense that the getter is only invoked once. Subsequent accesses
-    through *any* instance use the cached result.
-    """
-
-    def __init__(self, getter):
-        self.getter = getter
-        self.computed = False
-
-    def __get__(self, obj, owner):
-        if not self.computed:
-            self.value = self.getter(owner)
-            self.computed = True
-        return self.value
-
-
 @total_ordering
 class Distance:
     """Keeps track of multiple distance penalties. Provides a single
@@ -441,7 +424,7 @@ class Distance:
         self._penalties = {}
         self.tracks: Dict[TrackInfo, Distance] = {}
 
-    @LazyClassProperty
+    @cached_classproperty
     def _weights(cls) -> Dict[str, float]:  # noqa: N805
         """A dictionary from keys to floating-point weights."""
         weights_view = config["match"]["distance_weights"]

beets/util/__init__.py

@@ -1055,3 +1055,20 @@ def par_map(transform: Callable, items: Iterable):
     pool.map(transform, items)
     pool.close()
     pool.join()
+
+
+class cached_classproperty:  # noqa: N801
+    """A decorator implementing a read-only property that is *lazy* in
+    the sense that the getter is only invoked once. Subsequent accesses
+    through *any* instance use the cached result.
+    """
+
+    def __init__(self, getter):
+        self.getter = getter
+        self.cache = {}
+
+    def __get__(self, instance, owner):
+        if owner not in self.cache:
+            self.cache[owner] = self.getter(owner)
+
+        return self.cache[owner]

setup.cfg

@@ -31,7 +31,9 @@ show_contexts = true
 min-version = 3.8
 accept-encodings = utf-8
 max-line-length = 88
-docstring-convention = google
+classmethod-decorators =
+  classmethod
+  cached_classproperty
 # errors we ignore; see https://www.flake8rules.com/ for more info
 ignore =
     # pycodestyle errors

test/test_autotag.py

@@ -143,7 +143,7 @@ def _clear_weights():
     """Hack around the lazy descriptor used to cache weights for
     Distance calculations.
     """
-    Distance.__dict__["_weights"].computed = False
+    Distance.__dict__["_weights"].cache = {}
 
 
 class DistanceTest(_common.TestCase):