Managing thirdparty package: defer.

thirdparty/defer/_defer.py

@@ -0,0 +1,32 @@
+from contextlib import ExitStack
+from types import FrameType
+from typing import Any, Callable, Optional, ParamSpec, TypeVar
+
+
+P = ParamSpec("P")
+T = TypeVar("T")
+
+
+class _Defer:
+    def __init__(self, tracefn: Optional[Callable]) -> None:
+        self.tracefn = tracefn or (lambda *_: None)
+
+        self._stack = ExitStack()
+        self._stack.__enter__()
+
+    def push(self, fn: Callable[P, T], *args: P.args, **kwargs: P.kwargs):
+        self._stack.callback(fn, *args, **kwargs)
+
+    def __call__(self, frame: FrameType, event: str, arg: Any):
+        self.tracefn(frame, event, arg)
+
+        match event:
+            case "call":
+                self._stack.__enter__()
+            case "return":
+                self._stack.__exit__(None, None, None)
+                self._stack = ExitStack()
+            case "exception":
+                self._stack.__exit__(*arg)
+                self._stack = ExitStack()
+        return self