Add tool to catch the shadowing of _ (gettext)

[bmispelon]

With the fantastic work that's been going on to make the site translatable, we've been using the _ alias for gettext more and more throughout the codebase.

Unfortunately, the name _ is also sometimes used to create throwaway variables, and this can lead to crashes (see e995213).

It would be nice if he had a tool to warn us when reusing the name _ for a throwaway variable in a file that already has _ as an alias for gettext. I'm hoping there's already a flake8 plugin for it, or something similar.

[bmispelon]

@marksweb tagging you in just in case you know of existing solutions. This is something I didn't think of when doing the code review, I'll try to pay more attention next time.

[marksweb]

Oh sorry I missed this one.

Historically when I've had this issue I change the import alias because the underscore is the unused variable standard.

[bmispelon]

For now I've used git grep -E '\b_[^(_a-zA-Z9-9]' -- '*.py' to check for usage of the throwaway _ variable and I'm confident that we don't have other instances of this error currently.

I've looked around a bit and haven't found any available plugins, so this might need to be custom-made 🤔

[marksweb]

@bmispelon yeah I've not found anything either. Could likely set that up as a workflow action to run on PRs