Ignore specific lines

[Shookit]

I don't know if this is intentionally omitted, or if I'm just not aware of the functionality, but is there any way to ignore mypy errors line-by-line?

For instance, one of the files I'm using mypy on works, but for certain lines...

graph.py, line 3: No module named 'numpy'
graph.py, line 4: No module named 'matplotlib.pyplot'
graph.py, line 5: No module named 'scipy.stats'
graph.py, line 155: Unexpected keyword argument "key" for "max"

...mypy gives errors incorrectly that I'd like to ignore (the modules do exist, and max does take the 'key' argument).

Is there any way to skip these lines, such as in a linter, or a way to hint to mypy that these are valid?

[rockneurotiko]

Check this issue #486 , right now you can't, but there are some things to do before to allow that.

[JukkaL]

This is something that I'd like to have and have thought about it a little. A potential approach is to use a special comment for this:

import numpy  # mypy: ignore

We could also support an if statement for this (this actually partially implemented already but completely undocumented):

from typing import MYPY

if not MYPY:
    import numpy

The value of MYPY would always be False at runtime, but when type checking it would be considered as a compile-time constant with value True that could be used for a kind of conditional compilation -- a if not MYPY block would be ignored by the type checker (but any newly defined names would be given the type Any, perhaps).

Or maybe we can support using a comment to ignore multiple lines:

# mypy: begin ignore
import numpy
import matplotlib.pyplot
import scipy.stats
# mypy: end ignore

Implementation of #486 would be awesome but it does not help when there are C extension modules. However, we may be able to automatically generate pure dynamically typed stubs for C extension modules automatically. @ashleyh started writing a stub generator (I have a clone at https://github.com/JukkaL/mypy-stubgen) but there hasn't been updates in a long time.

[spkersten]

I like annotations to instruct mypy to ignore something much more than having to change code by adding if not MYPY guards.

[JukkaL]

PEP 484 uses # type: ignore for ignoring type errors on particular lines, and mypy should support that. Also, using # type: ignore close to the top of a file should skip checking that file altogether.

[JukkaL]

Okay, now you can use # type: ignore to silence some errors. Example:

import foo # type: ignore
foo.f()  # okay

[CMCDragonkai]

If the expression being ignored is spread out across lines, the ignore annotation doesn't work.

    with subprocess.Popen(
            *args, bufsize=1, stderr=subprocess.PIPE, **kwargs) as proc: # type: ignore