Support 'on'/'off' for type ignores

[wadetregaskis-linkedin]

Sometimes it's impossible to put # type: ignore on the offending line - e.g. because it's a multiline string, and there's nowhere you can put the comment outside the string that mypy will recognise. Or more generally, there might be a whole block of code for which mypy has a bunch of spurious complaints, so putting in dozens of # type: ignores is a bit noisy.

The only other option today is to have mypy ignore the entire file, but that has nasty ramifications - beyond just killing type checking for what might be 99% checkable, it also makes any imports of that file invalid, and so you have to spread ignore directives out like a messy spiderweb.

Thus, it'd be great if one could do e.g. # type: ignore on and # type: ignore off, so that the scope could be controlled precisely.

[wadetregaskis-linkedin]

Related: #9484

[hauntsaninja]

Related, also mentions typing.no_type_check: #6948

[wadetregaskis-linkedin]

Awesome, I didn't know no_type_check existed. That's a much better workaround than the others I knew of. It's not quite as nice as what I requested here, but it's close - I just have to wrap the code in question in a dummy, nested function in order to be able to apply the decorator. Silly enough that it requires a comment documenting it, but quite functional otherwise.

Sidenote: no_type_check in name sounds clear, but the documentation for it is super misleading. "Decorator to indicate that annotations are not type hints."… wot? That doesn't sound like what it actually does at all.

[gvanrossum]

Could you send a PR that updates the docs to your liking? I agree that phrasing is odd -- it comes from the early days of discussion about PEP 484, when there appeared to be a substantial (or at least vocal) minority of Python users who didn't want to use annotations for types because they already had some other (ab)use in mind.