Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (4188188) to head (32af4fd).
Report is 1 commits behind head on master.

@@            Coverage Diff            @@
##            master      #251   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            4         4           
  Lines          525       526    +1     
  Branches        97        97           
=========================================
+ Hits           525       526    +1     

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I actually only tried MYPY. My interpretation of mypy docs is that only MYPY is officially promised to work here, and TYPE_CHECKING only when imported from typing.

Let's do python/mypy#18443 :-)
https://github.com/python/mypy/blob/master/mypy/reachability.py#L152

Great! Switched to TYPE_CHECKING here.

According to my tests, making Output inherit from object rather than typing.NamedTuple doesn't hurt performance (of pure Python or mypyc whels), so merging this doesn't appear to have a downside.