You can probably annotateself with eitherExprSequence[Expr] orExprSequence[Any] ifExprSequence is invariant inE.

You are giving up some type safety, especially in the latter case, but that already goes out of the window to some degree due to the implicit reliance onExprSequence.__init__ never violating LSP in a subclass. You could instead rely on an alternate constructor classmethod, which is checked for LSP violations, to improve safety.

You could even try to use a method-scopedTypeVar for this alternate constructor, so it can be bound independently of the class scopedE. Although that would make the constructor less convenient to use, since you can't useSelf as the return type in that case.