Argument X of "Y" incompatible with supertype "Z" - needs more detail

[remdragon]

• Are you reporting a bug, or opening a feature request?

feature request. Presumably mypy has the type information from the supertype available and at hand. It would be extremely helpful if that information was included in the diagnostics so that I don't have to go hunting for it.

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

import datetime
class Tzoffset ( datetime.tzinfo ):
	_delta = _tzname = None
	def __init__ ( self, delta, tzname='' ):
		# type: ( datetime.timedelta, str ) -> None
		assert isinstance ( delta, datetime.timedelta )
		self._delta = delta
		self._tzname = tzname
	def utcoffset ( self, dt ):
		# type: ( datetime.datetime ) -> datetime.timedelta
		return self._delta
	def dst ( self, dt ):
		# type: ( datetime.datetime ) -> datetime.timedelta
		return self._delta
	def tzname ( self, dt ):
		# type: ( datetime.datetime ) -> str
		return self._tzname

• What is the actual behavior/output?

error: Argument 1 of "tzname" incompatible with supertype "tzinfo"

• What is the behavior/output you expect?

error: Argument 1 of "tzname" incompatible with supertype "tzinfo"; expected "foo"

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 20:19:30) [MSC v.1500 32 bit (Intel)] on win32
Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:04:45) [MSC v.1900 32 bit (Intel)] on win32
mypy 0.600
dunno how to check git master

• What are the mypy flags you are using? (For example --strict-optional)

mypy --py2 %1 --ignore-missing-imports --disallow-untyped-defs
mypy %1 --ignore-missing-imports --disallow-untyped-defs

• If mypy crashed with a traceback, please paste
  the full traceback below.

(n/a)

[ilevkivskyi]

Note there is a proposal to add more info for errors like this behind a flag #4835

[remdragon]

This is what I ended up doing to shut up mypy, but it's not correct: def tzname ( self, dt ): # type: ( Any ) -> Optional[str] # TODO FIXME: figure out the correct type for the 1st argument return self._tzname.encode ( 'ascii' ) Royce Mitchell, IT Consultant ITAS Solutions royce3@itas-solutions.com

…

On Mon, May 21, 2018 at 9:19 AM, vovanz ***@***.***> wrote: @remdragon <https://github.com/remdragon> did you figured out what type does mypy expects as the first argument to tzname method? I've encountered this problem as well. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#5025 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADka13OWJb4b6w11v4vxRYSkVqlLLFEDks5t0szWgaJpZM4T8pxH> .

[matys18]

Taking a look at this