pyupgrade: rewrite `yield` statements in a loop to `yield from` This is the `legacy` fixer in `pyupgrade`, with the `yield` statement yielding loop commented back in. This seems to help pytype in some cases, and hurt it in others. But that can be manually fixed later. Note that it's possibly buggy in that it aggressively changed `import-checker.py` to `yield from 'fcntl', 'grp', 'pwd', 'select', 'termios': # Unix only`, which is invalid syntax. Possibly it needed help from the token fixer that I've disabled locally (because that wants to make a bunch of unrelated changes). Just change those few places to yield from a list, to avoid having to constantly revert that.