FeatureNames doesn't support slicing about eli5

[lopuhin]

Nice catch!
I tried a negative slice in python 2, and it turns it into a non-negative slice, so it should be easy to support it here too. ok, it does not always happen :)
That slice operation should return a new FeatureNames object, right?

[kmike]

That slice operation should return a new FeatureNames object, right?

A good question; I think that's fine to return a list if returning FeatureUnion is harder to implement.

[lopuhin]

Hm, I didn't think about it at first (was going to make it return FeatureUnion), but in fact it will make implementation more complex - for example, we still might have missing entries that are handled by unkn_template, but now the index must be shifted.
So I agree, let's go with returning a list (or maybe a numpy slice if the underlying storage is a numpy array)