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Comment by lacker | Hacker News Reader

That's a good point, for example in Eigen you can do

Eigen::Matrix<float, 10, 5>

I just really want it in Python because that's where I do most of my matrix manipulation nowadays. I guess you also would really like it to handle non-constants. It would be nice if these complicated library functions like

torch.nn.MultiheadAttention(embed_dim, num_heads, dropout=0.0, bias=True, add_bias_kv=False, add_zero_attn=False, kdim=None, vdim=None, batch_first=False, device=None, dtype=None)

would actually typecheck that kdim and vdim are correct, and ensure that I correctly pass a K x V matrix and not a V x K one.

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Python is a dynamic language where everything happens at run time, including checks of variable types. So you can already do this.

Python has static typechecking which, while not perfect, works pretty well as long as you're not actually trying to circumvent it (or manipulating things "too dynamically")

I think Python actually has multiple, different static typechecking systems, depending on which checker you use.

Python itself only gives you type annotations, but doesn't specify what they are supposed to mean.

(I think. Please correct me if I am wrong.)

You are slightly wrong.

Python does allow you to put anything in annotations. ( pep 3107 that defines type annotations says that explicitly [1]).

But it also defines a type checking annotations, which is a specific convention for using pep 3107 annotations. Type annotations were introduced in PEP 484 and updated in a lot of subsequent peps. The python typing system is fully specified in [3].

It does have several implementations, although the reference implementation is mypy

[1]: https://peps.python.org/pep-3107/#rejected-proposals

[2]: https://peps.python.org/pep-0484/

[3]: https://typing.python.org/en/latest/spec/index.html

The problem with runtime is when you make a mistake it can be a long time before you find out. Compile time means a large class of problems is prevented without perfect test coverage. On a small project it isn't a big deal but when you have hundgeds of developers over decades you will miss something

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