The underlying email.generator.BytesGenerator is documented as requiring an
fp that accepts bytes, so I'm not sure why pytype is getting confused:
File "/mnt/c/Users/Matt/hg/mercurial/patch.py", line 112, in msgfp: Function Generator.__init__ was called with the wrong arguments [wrong-arg-types] Expected: (self, outfp: TextIO, ...) Actually passed: (self, outfp: io.BytesIO, ...)