PydubLoader: Add helper class for SoundFileLoader to avoid repetition

There needs to be some class sitting between SoundFileLoader and the
concrete children since
 - each child shares a lot of code with siblings
 - each child needs the `pydub` external library, which may not exist
   on all systems

See #122 for more context.

ultratrace2/model/files/loaders/flac.py

@@ -1,28 +1,7 @@
-import pydub  # type: ignore
+from .pydub import PydubLoader
 
-from .base import FileLoadError, SoundFileLoader
 
-
-class FLACLoader(SoundFileLoader):
-    def get_path(self) -> str:
-        return self._path
-
-    def set_path(self, path) -> None:
-        self._path = path
-
-    def __init__(self, path: str, audio_segment: pydub.AudioSegment):
-        self.set_path(path)
-        self.audio_segment = audio_segment
-
-    def __len__(self) -> int:
-        return len(self.audio_segment)
-
-    @classmethod
-    def from_file(cls, path: str) -> "FLACLoader":
-        try:
-            audio_segment = pydub.AudioSegment.from_file(path)
-            return FLACLoader(path, audio_segment)
-        except Exception as e:
-            raise FileLoadError(
-                f"Invalid FLAC ({path}), unable to read: {str(e)}"
-            ) from e
+class FLACLoader(PydubLoader):
+    @staticmethod
+    def get_priority() -> int:
+        return 4

ultratrace2/model/files/loaders/mp3.py

@@ -1,28 +1,7 @@
-import pydub  # type: ignore
+from .pydub import PydubLoader
 
-from .base import FileLoadError, SoundFileLoader
 
-
-class MP3Loader(SoundFileLoader):
-    def get_path(self) -> str:
-        return self._path
-
-    def set_path(self, path) -> None:
-        self._path = path
-
-    def __init__(self, path: str, audio_segment: pydub.AudioSegment):
-        self.set_path(path)
-        self.audio_segment = audio_segment
-
-    def __len__(self) -> int:
-        return len(self.audio_segment)
-
-    @classmethod
-    def from_file(cls, path: str) -> "MP3Loader":
-        try:
-            audio_segment = pydub.AudioSegment.from_file(path)
-            return MP3Loader(path, audio_segment)
-        except Exception as e:
-            raise FileLoadError(
-                f"Invalid MP3 ({path}), unable to read: {str(e)}"
-            ) from e
+class MP3Loader(PydubLoader):
+    @staticmethod
+    def get_priority() -> int:
+        return 1

ultratrace2/model/files/loaders/ogg.py

@@ -1,28 +1,7 @@
-import pydub  # type: ignore
+from .pydub import PydubLoader
 
-from .base import FileLoadError, SoundFileLoader
 
-
-class OggLoader(SoundFileLoader):
-    def get_path(self) -> str:
-        return self._path
-
-    def set_path(self, path) -> None:
-        self._path = path
-
-    def __init__(self, path: str, audio_segment: pydub.AudioSegment):
-        self.set_path(path)
-        self.audio_segment = audio_segment
-
-    def __len__(self) -> int:
-        return len(self.audio_segment)
-
-    @classmethod
-    def from_file(cls, path: str) -> "OggLoader":
-        try:
-            audio_segment = pydub.AudioSegment.from_file(path)
-            return OggLoader(path, audio_segment)
-        except Exception as e:
-            raise FileLoadError(
-                f"Invalid Ogg ({path}), unable to read: {str(e)}"
-            ) from e
+class OggLoader(PydubLoader):
+    @staticmethod
+    def get_priority() -> int:
+        return 2

ultratrace2/model/files/loaders/pydub.py

@@ -0,0 +1,26 @@
+import pydub  # type: ignore
+
+from .base import FileLoadError, SoundFileLoader
+
+
+class PydubLoader(SoundFileLoader):
+    def get_path(self) -> str:
+        return self._path
+
+    def set_path(self, path) -> None:
+        self._path = path
+
+    def __init__(self, path: str, audio_segment: pydub.AudioSegment):
+        self.set_path(path)
+        self.audio_segment = audio_segment
+
+    def __len__(self) -> int:
+        return len(self.audio_segment)
+
+    @classmethod
+    def from_file(cls, path: str) -> "PydubLoader":
+        try:
+            audio_segment = pydub.AudioSegment.from_file(path)
+            return PydubLoader(path, audio_segment)
+        except Exception as e:
+            raise FileLoadError(f"Invalid AudioSegment ({path}), unable to read") from e

ultratrace2/model/files/loaders/wav.py

@@ -1,28 +1,7 @@
-import pydub  # type: ignore
+from .pydub import PydubLoader
 
-from .base import FileLoadError, SoundFileLoader
 
-
-class WAVLoader(SoundFileLoader):
-    def get_path(self) -> str:
-        return self._path
-
-    def set_path(self, path) -> None:
-        self._path = path
-
-    def __init__(self, path: str, audio_segment: pydub.AudioSegment):
-        self.set_path(path)
-        self.audio_segment = audio_segment
-
-    def __len__(self) -> int:
-        return len(self.audio_segment)
-
-    @classmethod
-    def from_file(cls, path: str) -> "WAVLoader":
-        try:
-            audio_segment = pydub.AudioSegment.from_file(path)
-            return WAVLoader(path, audio_segment)
-        except Exception as e:
-            raise FileLoadError(
-                f"Invalid WAV ({path}), unable to read: {str(e)}"
-            ) from e
+class WAVLoader(PydubLoader):
+    @staticmethod
+    def get_priority() -> int:
+        return 3