[Mehdi2277]

Partly motivated? The primary focus was ML space. The creators of PEP 646 work at Facebook with goal of supporting pytorch tensor dimension tracking. That was main motivation and many of the features/design of that pep were based on what's needed to type hint tensor dimensions.

Pep was originally even longer and there's planned follow up peps for other tensor related type features like literal arithmetic to allow type hinting function like np.concatenate. I expect 2/3 more peps in that area in the next year or two.

[davidatbu]

Absolutely right about ML being the main motivation. The PEP says:

    The main case this PEP targets - concerns typing in numerical libraries.

However, despite the authors of the PEP working at facebook, the Pytorch team, at facebook, wasn't interested at all in the PEP. This is also from the PEP:

    For the sake of transparency - we also reached out to folks from a third popular numerical computing library, PyTorch, but did not receive a statement of endorsement from them. Our understanding is that although they are interested in some of the same issues - e.g. static shape inference - they are currently focusing on enabling this through a DSL rather than the Python type system