Adding type hints to OpenStack (starting with Oslo)

Doug Hellmann doug at
Sat Jan 26 18:29:29 UTC 2019

I agree with your concerns about code churn. I think it’s still useful to run a small experiment to demonstrate how we might actually benefit from them though, which applying them to one library would let us do. 

> On Jan 26, 2019, at 1:18 PM, Morgan Fainberg <morgan.fainberg at> wrote:
> Honestly, I would wait for this for the U release. We can then go to the annotation style and if needed update docstrings at the same time. My concern with pushing this now is a high churn of code that should be duplicated once we drop PY2 support.
> Other than my above concerns the type checking in mypy would be great to have. 
> --Morgan
>> On Sat, Jan 26, 2019, 09:14 Sergey Vilgelm <sergey at wrote:
>> Cyril,
>> We have lots of doc strings in rst format and many of them already have the `@param` and `@type` tags. Does the mypy support this format or we should to rewrite doc string and add the `type:` tags just for mypy?
>> --
>> Sergey Vilgelm
>>> On Jan 26, 2019, 9:07 AM -0600, Cyril Roelandt <cyril at>, wrote:
>>> Hello Doug,
>>>> On 01/26/19 09:02, Doug Hellmann wrote:
>>>> We're still required to support python 2 through the beginning of the U
>>>> cycle [5]. Is it possible to apply the type hints in a way that allows
>>>> us to maintain that support?
>>>> [5]
>>> There are two ways to apply type hints:
>>> 1) Use a new syntax that only works with Python 3
>>> 2) Use comments (see my github branch, where comments starting with
>>> "type:" can be found)
>>> I used the second approach in order to not break Python 2 compatibility.
>>> Regards,
>>> Cyril
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