Raise NotImplementedError if using wrong class

docs/changelog.rst

@@ -1,6 +1,13 @@
 Changelog
 =========
 
+Future
+------
+- Fix pylint warning "Abstract class :class:`WindowsFileLock <filelock.WindowsFileLock>` with abstract methods instantiated"
+  :pr:`135` - by :user:`vonschultz`
+- Fix pylint warning "Abstract class :class:`UnixFileLock <filelock.UnixFileLock>` with abstract methods instantiated"
+  :pr:`135` - by :user:`vonschultz`
+
 v3.4.2 (2021-12-16)
 -------------------
 - Drop support for python ``3.6``

src/filelock/_unix.py

@@ -2,7 +2,6 @@
 
 import os
 import sys
-from abc import ABC
 from typing import cast
 
 from ._api import BaseFileLock
@@ -11,9 +10,15 @@
 has_fcntl = False
 if sys.platform == "win32":  # pragma: win32 cover
 
-    class UnixFileLock(BaseFileLock, ABC):
+    class UnixFileLock(BaseFileLock):
         """Uses the :func:`fcntl.flock` to hard lock the lock file on unix systems."""
 
+        def _acquire(self) -> None:
+            raise NotImplementedError
+
+        def _release(self) -> None:
+            raise NotImplementedError
+
 else:  # pragma: win32 no cover
     try:
         import fcntl

src/filelock/_windows.py

@@ -2,7 +2,6 @@
 
 import os
 import sys
-from abc import ABC
 from errno import ENOENT
 from typing import cast
 
@@ -49,9 +48,15 @@ def _release(self) -> None:
 
 else:  # pragma: win32 no cover
 
-    class WindowsFileLock(BaseFileLock, ABC):
+    class WindowsFileLock(BaseFileLock):
         """Uses the :func:`msvcrt.locking` function to hard lock the lock file on windows systems."""
 
+        def _acquire(self) -> None:
+            raise NotImplementedError
+
+        def _release(self) -> None:
+            raise NotImplementedError
+
 
 __all__ = [
     "WindowsFileLock",

tests/test_filelock.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import inspect
 import logging
 import sys
 import threading
@@ -13,7 +14,7 @@
 import pytest
 from _pytest.logging import LogCaptureFixture
 
-from filelock import BaseFileLock, FileLock, SoftFileLock, Timeout
+from filelock import BaseFileLock, FileLock, SoftFileLock, Timeout, UnixFileLock, WindowsFileLock
 
 
 @pytest.mark.parametrize(
@@ -368,3 +369,35 @@ def test_poll_intervall_deprecated(lock_type: type[BaseFileLock], tmp_path: Path
                 break
         else:  # pragma: no cover
             pytest.fail("No warnings of stacklevel=2 matching.")
+
+
+@pytest.mark.skipif(sys.platform != "win32", reason="Tests behavior of UnixFileLock on Windows systems")
+def test_unix_lock_on_windows(tmp_path: Path) -> None:
+    lock = UnixFileLock(str(tmp_path / "lockfile"))
+
+    assert not inspect.isabstract(
+        UnixFileLock
+    ), "UnixFileLock must not be an abstract class, or pylint will complain in client code"
+    assert inspect.isabstract(BaseFileLock)
+
+    with pytest.raises(NotImplementedError):
+        lock.acquire()
+
+    with pytest.raises(NotImplementedError):
+        lock._release()
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="Tests behavior of WindowsFileLock on non-Windows systems")
+def test_windows_lock_on_unix(tmp_path: Path) -> None:
+    lock = WindowsFileLock(str(tmp_path / "lockfile"))
+
+    assert not inspect.isabstract(
+        WindowsFileLock
+    ), "WindowsFileLock must not be an abstract class, or pylint will complain in client code"
+    assert inspect.isabstract(BaseFileLock)
+
+    with pytest.raises(NotImplementedError):
+        lock.acquire()
+
+    with pytest.raises(NotImplementedError):
+        lock._release()