I don't like co_annotations.

* It changes PyCode_NewXXX() API.

* Many functions don't have annotations. Adding annotation to code object makes code object fatter even if the function doesn't have annotation.

* Code object is immutable & hashable. Adding annotation to code object makes == and hash() complex.

* We may introduce lazy loading for docstring and annotation in the future.


func.__annotations__ =  ('x', 'int', 'z', 'float', 'return', 'Hoge') is much better because:

* Zero overhead for functions without any annotations.
* After annotation dict is created, the tuple can be released.