Move nested class out of the parent class

Removing nested classes avoids having to use hacky constructions, like
requiring the use of `from __future__ import annotations`, types as
strings and confusing the `mkdocstrings` tools when extracting and
cross-linking docs.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

src/frequenz/channels/_select.py

@@ -17,6 +17,16 @@
 _T = TypeVar("_T")
 
 
+class _EmptyResult:
+    """A sentinel value to distinguish between None and empty result.
+
+    We need a sentinel because a result can also be `None`.
+    """
+
+    def __repr__(self) -> str:
+        return "<empty>"
+
+
 class Selected(Generic[_T]):
     """A result of a [`select()`][frequenz.channels.select] iteration.
 
@@ -31,15 +41,6 @@ class Selected(Generic[_T]):
     Please see [`select()`][frequenz.channels.select] for an example.
     """
 
-    class _EmptyResult:
-        """A sentinel value to distinguish between None and empty result.
-
-        We need a sentinel because a result can also be `None`.
-        """
-
-        def __repr__(self) -> str:
-            return "<empty>"
-
     def __init__(self, receiver: Receiver[_T]) -> None:
         """Create a new instance.
 
@@ -55,7 +56,7 @@ def __init__(self, receiver: Receiver[_T]) -> None:
         self._recv: Receiver[_T] = receiver
         """The receiver that was selected."""
 
-        self._value: _T | Selected._EmptyResult = Selected._EmptyResult()
+        self._value: _T | _EmptyResult = _EmptyResult()
         """The value that was received.
 
         If there was an exception while receiving the value, then this will be `None`.
@@ -86,7 +87,7 @@ def value(self) -> _T:
         """
         if self._exception is not None:
             raise self._exception
-        assert not isinstance(self._value, Selected._EmptyResult)
+        assert not isinstance(self._value, _EmptyResult)
         return self._value
 
     @property

src/frequenz/channels/file_watcher.py

@@ -3,8 +3,6 @@
 
 """A Channel receiver for watching for new, modified or deleted files."""
 
-from __future__ import annotations
-
 import asyncio
 import pathlib
 from collections import abc
@@ -17,29 +15,31 @@
 from ._receiver import Receiver, ReceiverStoppedError
 
 
-class FileWatcher(Receiver["FileWatcher.Event"]):
-    """A channel receiver that watches for file events."""
+class EventType(Enum):
+    """Available types of changes to watch for."""
+
+    CREATE = Change.added
+    """A new file was created."""
 
-    class EventType(Enum):
-        """Available types of changes to watch for."""
+    MODIFY = Change.modified
+    """An existing file was modified."""
 
-        CREATE = Change.added
-        """A new file was created."""
+    DELETE = Change.deleted
+    """An existing file was deleted."""
 
-        MODIFY = Change.modified
-        """An existing file was modified."""
 
-        DELETE = Change.deleted
-        """An existing file was deleted."""
+@dataclass(frozen=True)
+class Event:
+    """A file change event."""
 
-    @dataclass(frozen=True)
-    class Event:
-        """A file change event."""
+    type: EventType
+    """The type of change that was observed."""
+    path: pathlib.Path
+    """The path where the change was observed."""
 
-        type: FileWatcher.EventType
-        """The type of change that was observed."""
-        path: pathlib.Path
-        """The path where the change was observed."""
+
+class FileWatcher(Receiver[Event]):
+    """A channel receiver that watches for file events."""
 
     def __init__(
         self,
@@ -53,7 +53,7 @@ def __init__(
             event_types: Types of events to watch for. Defaults to watch for
                 all event types.
         """
-        self.event_types: frozenset[FileWatcher.EventType] = frozenset(event_types)
+        self.event_types: frozenset[EventType] = frozenset(event_types)
         """The types of events to watch for."""
 
         self._stop_event: asyncio.Event = asyncio.Event()
@@ -133,9 +133,7 @@ def consume(self) -> Event:
         assert self._changes, "`consume()` must be preceded by a call to `ready()`"
         # Tuple of (Change, path) returned by watchfiles
         change, path_str = self._changes.pop()
-        return FileWatcher.Event(
-            type=FileWatcher.EventType(change), path=pathlib.Path(path_str)
-        )
+        return Event(type=EventType(change), path=pathlib.Path(path_str))
 
     def __str__(self) -> str:
         """Return a string representation of this receiver."""

tests/test_file_watcher.py

@@ -15,7 +15,7 @@
 from watchfiles import Change
 from watchfiles.main import FileChange
 
-from frequenz.channels.file_watcher import FileWatcher
+from frequenz.channels.file_watcher import Event, EventType, FileWatcher
 
 
 class _FakeAwatch:
@@ -74,14 +74,14 @@ async def test_file_watcher_receive_updates(
 
     for change in changes:
         recv_changes = await file_watcher.receive()
-        event_type = FileWatcher.EventType(change[0])
+        event_type = EventType(change[0])
         path = pathlib.Path(change[1])
-        assert recv_changes == FileWatcher.Event(type=event_type, path=path)
+        assert recv_changes == Event(type=event_type, path=path)
 
 
-@hypothesis.given(event_types=st.sets(st.sampled_from(FileWatcher.EventType)))
+@hypothesis.given(event_types=st.sets(st.sampled_from(EventType)))
 async def test_file_watcher_filter_events(
-    event_types: set[FileWatcher.EventType],
+    event_types: set[EventType],
 ) -> None:
     """Test the file watcher events filtering."""
     good_path = "good-file"
@@ -100,7 +100,7 @@ async def test_file_watcher_filter_events(
                 pathlib.Path(good_path), stop_event=mock.ANY, watch_filter=filter_events
             )
         ]
-        for event_type in FileWatcher.EventType:
+        for event_type in EventType:
             assert filter_events(event_type.value, good_path) == (
                 event_type in event_types
             )

tests/test_file_watcher_integration.py

@@ -10,7 +10,7 @@
 import pytest
 
 from frequenz.channels import select, selected_from
-from frequenz.channels.file_watcher import FileWatcher
+from frequenz.channels.file_watcher import Event, EventType, FileWatcher
 from frequenz.channels.timer import Timer
 
 
@@ -33,12 +33,8 @@ async def test_file_watcher(tmp_path: pathlib.Path) -> None:
         if selected_from(selected, timer):
             filename.write_text(f"{selected.value}")
         elif selected_from(selected, file_watcher):
-            event_type = (
-                FileWatcher.EventType.CREATE
-                if number_of_writes == 0
-                else FileWatcher.EventType.MODIFY
-            )
-            assert selected.value == FileWatcher.Event(type=event_type, path=filename)
+            event_type = EventType.CREATE if number_of_writes == 0 else EventType.MODIFY
+            assert selected.value == Event(type=event_type, path=filename)
             number_of_writes += 1
             # After receiving a write 3 times, unsubscribe from the writes channel
             if number_of_writes == expected_number_of_writes:
@@ -58,9 +54,7 @@ async def test_file_watcher_deletes(tmp_path: pathlib.Path) -> None:
         tmp_path: A tmp directory to run the file watcher on. Created by pytest.
     """
     filename = tmp_path / "test-file"
-    file_watcher = FileWatcher(
-        paths=[str(tmp_path)], event_types={FileWatcher.EventType.DELETE}
-    )
+    file_watcher = FileWatcher(paths=[str(tmp_path)], event_types={EventType.DELETE})
     write_timer = Timer.timeout(timedelta(seconds=0.1))
     deletion_timer = Timer.timeout(timedelta(seconds=0.25))