Hotfix: Restore __init__ method; more robust initialization for singleton locks

src/filelock/_api.py

@@ -85,39 +85,32 @@ class BaseFileLock(ABC, contextlib.ContextDecorator):
     def __new__(  # noqa: PLR0913
         cls,
         lock_file: str | os.PathLike[str],
-        timeout: float = -1,
-        mode: int = 0o644,
-        thread_local: bool = True,  # noqa: FBT001, FBT002
+        timeout: float = -1,  # noqa: ARG003
+        mode: int = 0o644,  # noqa: ARG003
+        thread_local: bool = True,  # noqa: FBT001, FBT002, ARG003
         *,
-        blocking: bool = True,
+        blocking: bool = True,  # noqa: ARG003
         is_singleton: bool = False,
         **kwargs: Any,  # capture remaining kwargs for subclasses  # noqa: ARG003, ANN401
     ) -> Self:
         """Create a new lock object or if specified return the singleton instance for the lock file."""
         if not is_singleton:
-            self = super().__new__(cls)
-            self._initialize(lock_file, timeout, mode, thread_local, blocking=blocking, is_singleton=is_singleton)
-            return self
+            return super().__new__(cls)
 
         instance = cls._instances.get(str(lock_file))
         if not instance:
             self = super().__new__(cls)
-            self._initialize(lock_file, timeout, mode, thread_local, blocking=blocking, is_singleton=is_singleton)
             cls._instances[str(lock_file)] = self
             return self
 
-        if timeout != instance.timeout or mode != instance.mode:
-            msg = "Singleton lock instances cannot be initialized with differing arguments"
-            raise ValueError(msg)
-
         return instance  # type: ignore[return-value] # https://github.com/python/mypy/issues/15322
 
     def __init_subclass__(cls, **kwargs: dict[str, Any]) -> None:
         """Setup unique state for lock subclasses."""
         super().__init_subclass__(**kwargs)
         cls._instances = WeakValueDictionary()
 
-    def _initialize(  # noqa: PLR0913
+    def __init__(  # noqa: PLR0913
         self,
         lock_file: str | os.PathLike[str],
         timeout: float = -1,
@@ -143,6 +136,19 @@ def _initialize(  # noqa: PLR0913
             to pass the same object around.
 
         """
+        if is_singleton and hasattr(self, "_context"):
+            # test whether other parameters match existing instance.
+            if (
+                self.is_thread_local() != thread_local
+                or not self.is_singleton
+                or self._context.timeout != timeout
+                or self._context.mode != mode
+                or self._context.blocking != blocking
+            ):
+                msg = "Singleton lock instances cannot be initialized with differing arguments"
+                raise ValueError(msg)
+            return  # bypass initialization because object is already initialized
+
         self._is_thread_local = thread_local
         self._is_singleton = is_singleton
 

tests/test_filelock.py

@@ -687,9 +687,10 @@ def __init__(  # noqa: PLR0913 Too many arguments to function call (6 > 5)
             mode: int = 0o644,
             thread_local: bool = True,
             my_param: int = 0,
-            **kwargs: dict[str, Any],
+            **kwargs: dict[str, Any],  # noqa: ARG002
         ) -> None:
-            pass
+            super().__init__(lock_file, timeout, mode, thread_local, blocking=True, is_singleton=True)
+            self.my_param = my_param
 
     lock_path = tmp_path / "a"
     MyFileLock(str(lock_path), my_param=1)
@@ -702,9 +703,10 @@ def __init__(  # noqa: PLR0913 Too many arguments to function call (6 > 5)
             mode: int = 0o644,
             thread_local: bool = True,
             my_param: int = 0,
-            **kwargs: dict[str, Any],
+            **kwargs: dict[str, Any],  # noqa: ARG002
         ) -> None:
-            pass
+            super().__init__(lock_file, timeout, mode, thread_local, blocking=True, is_singleton=True)
+            self.my_param = my_param
 
     MySoftFileLock(str(lock_path), my_param=1)