Allow one to specify which packages to follow from command line and comments and which do not

[mitar]

I have a package A which imports multiple my package B, C and so on. All of the packages have typing annotations, but they are not public. I am trying to integrate mypy into my CI, where I install all dependencies for A and try to type check current code. The issue is that my other packages cannot be imported. On the other hand, if I use MYPYPATH to point it to site-packages directory where they were installed, mypy tries to type check many other packages which then fail (despite some of them having stubs, and other imports have # type: ignore next to them).

Now, reading documentation it seems that the expected thing would be that I generate stub files for other packages? But where do I put them? If I put them next to package files, then I have to point MYPYPATH to site-packages and we are again to square one. If I put them elsewhere, how do I easily get them through installation of requirements? Also, if my code is nicely typed, why should I be generating stub files at all and worry if they are in sync with code?

It seems that the other option would be to put my dependencies in a separate directory, but then I have to duplicate my dependencies installation and copying them into a separate directory, double work, especially because the first one is done automatically.

So I would suggest that:

• if import A has next to it a comment # type: ignore, that package is not even tried to be imported and analyzed
• that I could list on the command line, use things you find in MYPY, but just for package B, C, and so on (fragile, I have to keep this list manually)
• that if a standard library has stubs, it does not try to load it and analyze it

So maybe just the first and last suggestion would already work for me. If I see that some import is blowing up, I could just add # type: ignore to it and it wouldn't. And all standard libraries would keep working. And then only those other relevant imports of B and C would matter. In that case, it would be great if mypy could automatically load from sys.path. So that I would not have to run it with:

MYPYPATH=$(python -c 'import sys; print(":".join(sys.path))') mypy ...

[gvanrossum]

A problem with your proposed semantics for # type: ignore is that in general the presence of # type: ignore should not change the behavior of the checker -- it should only suppress errors generated on that line.

[mitar]

What about then # type: recursive ignore? :-) So to suppress any errors in imported modules as well. And then we can see the fact that checker does not go into import only as an optimization.

[gvanrossum]

If you want to ignore import foo you can put this in your mypy.ini file:

[mypy]
[mypy-foo]
follow-imports = skip

FWIW I think eventually what you want will be solved by the proposal here: python/typing#84 (comment) (or something like it).

[JukkaL]

The workaround discussed above seems good enough.