> Why would it require a metaclass? Rather than just: ...

Because I want the following to be true:

```
x = Struct[x=int, y=str](...)
assert isinstance(x, Struct)
assert isinstance(x, Struct[x=int, y=str])
assert not isinstance(x, Struct[x=int, y=int])
```


On Fri, Aug 14, 2020 at 5:27 PM David Mertz <mertz@gnosis.cx> wrote:

On Fri, Aug 14, 2020, 7:53 PM Caleb Donovick <donovick@cs.stanford.edu> wrote:
> I don't see what that can possible get you that `Struct(x=int, y=str)` doesn't.

Using `Struct(x=int, y=str)` requires a metaclass, where `Struct[x=int, y=str]` does not.

Why would it require a metaclass? Rather than just:

class Struct:
    def __init__(self, **kws): ...

Yes, that won't get you the MRO for T, but neither can __getitem__() on an entirely different object Struct.

A class factory is also an option, of course.