Sorry, there is some hidden back story here, which makes it a little tricky to do this.

In Facebook internally, we have a lint check that essentially complains if you don't have Python 3 compatibility imports. There are a few ways to suppress it, but the one that is suggested by the linter is adding a shebang line to the top that explicitly says python3, even if the intent is never to actually run the file as an executable.

Andres helpfully gave some more tips about the linter though:

• This linter will not complain if it finds a .python3 or .python2 file up the parent dirs. This also affects how flake8 treats your files.
• This linter will not complain if it finds any future import in a file (so you could do from future import print and it'll stop complaining).
• This linter will not complain if it finds a versioned python shebang in a file (e.g. #!/usr/bin/env python2.7, #!/usr/bin/env python2, #!/usr/bin/env python3, basically anything with that matches ^#!.*python[23])
• This linter will not complain if the file has @lint-ignore-evert PYTHON3COMPATIMPORTS.

I landed a PR that puts .python2 in our top level directory, which should shut this up. But that's the reason why people keep adding these shebangs.

Sweet! Thanks for the context, @ezyang! For future reference, the PR is #27214.

Thanks for the explanation!

@ezyang merged this pull request in 987e37b.