LGTM too. Just one question: the _impl suffix to the filename was suggested by @ngoldbaum for names where we'd otherwise have both a public and a private file (e.g. stride_tricks.py and _stride_tricks.py). In this case though, there's only a single private name. Wouldn't a regular _histograms.py look better here? (I'm not sure, it really is a question - naming is hard)

@rgommers I would argue that keeping all implementations in _<submodule>_impl.py would be more consistent. I think mixing names depending on the fact of exporting to top or/and local namespace could be a bit confusing.

# Let's assume "stuff" submodule exists

numpy/__init__.py  # imports top namespace items

# 1. variant - only top namespace items
numpy/lib/_stuff_impl.py  # hosts implementation, no doubt
or .../_stuff.py  #  alternative name in this case

# 2. variant - top namespace and local items
numpy/lib/_stuff_impl.py  # hosts implementation
numpy/lib/stuff.py  # defines local namespace, imports from impl

Okay, fair enough, that's a good argument. I'm happy to go with this. Nathan also approved, so let's roll with this. It's the kind of thing we can easily revisit and make consistent later if we change our minds.

In it goes, thanks again!