allow_none on Number-like traits.

[Carreau]

Would it be reasonable to have an allow_none kwarg on nuber-like traits ?

I raise the question for @jakevdp that have start/end traits for slicing a list, and having None would help a lot the logic of slicing.

[minrk]

Hm. I wouldn't think so - I would add a different trait for that.

[Carreau]

Hm. I wouldn't think so - I would add a different trait for that.

IntergerMaybeNone ? (sound haskell)

[minrk]

What's it for? Inside IPython, or use elsewhere? I don't think we have a need for it in IPython.

If it's specifically for use in slices, I might just call it SliceField. Part of the point of traitlets is they are extensible - it's totally reasonable to define your own traitlets in your own project that have their own validation behavior

[Carreau]

Thanks, we went with custom traitlets. Closing.