--silent-imports prevent my code from being checked

[sametmax]

I have a tests directory containing unit tests for code in a src dir.

Currently I can either:

• use --silent-imports and gets no warning for missing stubs in 3rd party library. But then any line using the code from src is not going to be checked.
• or not silent imports, but have my tox commands fails because missing stubs will make mypy return an error code.

I need a way to silence import error, but still have my imports to be followed and checked.

[gvanrossum]

I'm not sure I understand this feature request. (Though it seems there are others who do, so clearly you have something important here.) Do you want mypy to exit 0 if there are errors but they are all errors that would be suppressed by --silent-imports?

If I understand your setup correctly, I think the way you are supposed to use this with --silent-imports is to explicitly pass the source package's parent directory (presumably src in your case) when type-checking the tests. But I can't confirm this without seeing exactly how you are invoking mypy, and what is in the various directories in your project. Is your project open source?

[ddfisher]

Are you interested in silencing errors from one import in particular? You can do that with #type: ignore, e.g.:

import module_without_stubs  # type: ignore

This will cause mypy to ignore the import error on that particular line.

[sametmax]

@ddfisher: I can do that for the 10 imports of my 20 files, but that's not really a clean way of doing it, isn't it?

@gvanrossum: i'll give more details in a minute.

[sametmax]

So I have code in dirs:

• src/ww
• tests

I run mypy by doing:

mypy tests/ --warn-unused-ignores --check-untyped-defs

When I do, I get type errors related to my use of the code from ww in tests such as:

"ww.IterableWrapper" expects no type arguments, but 1 given

And this is great, this is what I want.

However, doing so will also give me errors caused by 3rd party libraries such as:

error: No library stub file for module 'pytest'

Because pytest has no stubs. Or:

error: Cannot find module named 'past.builtins'

Because site-packages is (as suggested by the mypy doc) not in MYPYPATH.

The problems with those errors is that:

• I can't fix them. I won't write all stubs for pytest, nor include each dependencies of my project in MYPYPATH.
• Those errors remains when I fixed all errors that matter to me, such as real type errors on my part;
• mypy return an error code, making my CI process fails.

I can silence those errors with:

mypy tests/ --warn-unused-ignores --check-untyped-defs --silent-imports

But doing so will also prevent mypy from following imports from src/ww, despite src being explicitly in MYPYPATH. Suddenly, mypy doesn't check the lines of code in tests using src/ww objects, and so I can't see any warning about the type errors I made.

error: No library stub file for module 'pytest' disapears, but so does "ww.IterableWrapper" expects no type arguments, but 1 given, and half of my code is now unchecked.

[gvanrossum]

OK, so a reasonable feature would presumably a flag that silences complaints about totally missing imports (like pytest or past) but doesn't have the other effect of `--silent-imports` (which is to require stubs for modules not explicitly listed on the command line). I do think that in the meantime, most of your problems should go away if you simply run `mypy tests --silent-imports src/ww <flags>` since that will explicitly check all .py files in src/www.

[sametmax]

OK, so a reasonable feature would presumably a flag that silences complaints about totally missing imports.

You'd probably want 2 flags, --silence-missing-stubs and --silence-import-error, so that people can select to ignore missing stubs, but be warned if they are forgetting to include an import, or vice-versa.

But a better approach would be the one used in most popular linters such as flake8, pylint, etc: each type of errors have a code, and you can pass the ones you wish to ignore as a coma separated list using either the command line, a code comment or a config file. Each code is also displayed at the begining of each respective warning in the tool output, so that you can grep for it easily.

This would be a more general way of solving this problem:

• it works with one flag instead of many;
• it's flexible enough to cover potential future new use cases;
• with the config file, you can commit it in your VCS and share the checks you wish to apply with your team.

In the mean time I can just create a wrapper on top of mypy that filter out stdin manually an include it in the source.

P.S: This doesn't seem to work:

$ mypy tests --silent-imports src/ww  

usage: mypy [-h] [-v] [-V] [--python-version x.y] [--platform PLATFORM] [-2]
            [-s] [--almost-silent] [--disallow-untyped-calls]
            [--disallow-untyped-defs] [--check-untyped-defs]
            [--disallow-subclassing-any] [--warn-incomplete-stub]
            [--warn-redundant-casts] [--warn-unused-ignores]
            [--hide-error-context] [--fast-parser] [-i] [--cache-dir DIR]
            [--strict-optional]
            [--strict-optional-whitelist [GLOB [GLOB ...]]] [--pdb]
            [--show-traceback] [--stats] [--inferstats]
            [--custom-typing MODULE] [--scripts-are-modules]
            [--config-file CONFIG_FILE] [--show-column-numbers]
            [--xslt-html-report DIR] [--txt-report DIR]
            [--xslt-txt-report DIR] [--linecount-report DIR]
            [--html-report DIR] [--memory-xml-report DIR]
            [--old-html-report DIR] [--xml-report DIR]
            [--linecoverage-report DIR] [-m MODULE] [-c PROGRAM_TEXT]
            [-p PACKAGE]
            [files [files ...]]
mypy: error: unrecognized arguments: src/ww

[gvanrossum]

The "code" idea is a good one, but also one that will require a lot of changes to mypy, and it may not even work (there just are so many errors that mypy can emit). In any case it requires a separate issue to track as an idea.

[sametmax]

Let me open the ticket.

[sametmax]

Should we close this one in favor of the other? If it's too much work, the second may never come to existence, while the first solution would.

[gvanrossum]

In the short term this one is much more actionable (in fact I recommend that you try giving it a shot). Basically there are two places that check for silent_imports, they should probably check different flags (and silent_imports may have to imply both those other flags). Also see almost_silent. All the code is in mypy/build.py.

[sametmax]

Ok, I'll have a look if my client give me some time for this.

[gvanrossum]

Have a look at PR #2513. I think this will help you distinguish between the two meanings of --silent-import.

[gvanrossum]

So the new release (0.470) has these new flags instead of --silent-imports. There's --ignore-missing imports and there's separately --follow-imports={normal,silent,skip,error}. In particular "silent" is a behavior that the old --silent-imports couldn't do. These can also be specified on a per-module basis in the mypy.ini config file.

@sametmax I'm closing this issue now because I don't think we're going to be able to do much more about this. If you still have a scenario that you can't solve using the new flags please open a new issue!