my.time.tz: implement different policies for localizing

my/core/common.py

@@ -273,7 +273,8 @@ class classproperty(Generic[_R]):
 #     def __get__(self) -> _R:
 #         return self.f()
 
-# TODO maybe use opaque mypy alias?
+# for now just serves documentation purposes... but one day might make it statically verifiable where possible?
+# TODO e.g. maybe use opaque mypy alias?
 tzdatetime = datetime
 
 

my/core/error.py

@@ -15,6 +15,11 @@ ResT = Union[T, E]
 Res = ResT[T, Exception]
 
 
+def notnone(x: Optional[T]) -> T:
+    assert x is not None
+    return x
+
+
 def unwrap(res: Res[T]) -> T:
     if isinstance(res, Exception):
         raise res