How to enable mypy to detect the current virtualenv I am using?

[ChenZhongPu]

By default, mypy only checks the third-party libraries in the same virtualenv.

For example, if you are running your code in a virtualenv, make sure to install and use mypy within the virtualenv. Alternatively, if you want to use a globally installed mypy, set the --python-executable command line flag to point the Python interpreter containing your installed third party packages.

How to enable it to detect the current virtualenv I am using and then pass the correct path through --python-executable?

[ChenZhongPu]

This can be a good improvement for null-ls. And the following is a feasible solution for both macOS and Linux (I don't own a Windows machine):

In mypy.lua,

local virtual = os.getenv("VIRTUAL_ENV") or os.getenv("CONDA_DEFAULT_ENV") or "/usr"

-- below line 27
"--python-executable=" .. virtual .. "/bin/python3",

[jose-elias-alvarez]

This seems like a reasonable user modification, but I think there are too many possible cases for us to consider including this as a default. You're free to make the change locally, either directly in the source or by modifying the built-in's arguments.