Issues

• x in y doesn't report errors when x is not str and y: union | involving | str

  bugtopic-union-types
  python/mypy#21595 · Filter by author bzoracler opened on Jun 5, 2026
  1

• Self type is not expanded correctly when accessed on a type variable with union bound

  bugtopic-self-typestopic-type-variablestopic-union-types
  python/mypy#19584 · Filter by author jorgefandinno opened on Aug 4, 2025

• func-returns-value false positive for union type?

  bugtopic-callstopic-union-types
  python/mypy#19433 · Filter by author asottile opened on Jul 13, 2025
  1

• Type checking fails to distribute across Tuple types

  bugfalse-positivetopic-union-types
  python/mypy#18922 · Filter by author bcmills opened on Apr 14, 2025
  10

• Union of Never can't be used

  bugtopic-union-types
  python/mypy#18779 · Filter by author pleaseletmesearch opened on Mar 10, 2025
  3

• mypy throws assignment error for a list created from an empty list

  featuretopic-type-variablestopic-union-types
  python/mypy#18735 · Filter by author Felixoid opened on Feb 25, 2025
  2

• False negative when lvalue has union type

  affects-mypycbugtopic-union-types
  python/mypy#17859 · Filter by author JukkaL opened on Oct 1, 2024

• Generic matching error when tuple-unpacking result

  bugtopic-inferencetopic-type-variablestopic-union-types
  python/mypy#16310 · Filter by author msullivan opened on Oct 21, 2023

• Union of Literals as key in union of TypedDict false positive

  bugtopic-typed-dicttopic-union-types
  python/mypy#14459 · Filter by author connesy opened on Jan 16, 2023
  4

• Incorrect handling of unions of generics

  bugtopic-type-variablestopic-union-types
  python/mypy#14403 · Filter by author hauntsaninja opened on Jan 6, 2023
  1

• (🎁) Perform 'union math' on non overloaded calls

  featuretopic-type-variablestopic-union-types
  python/mypy#13493 · Filter by author KotlinIsland opened on Aug 24, 2022
  2

• Argument type Union[T, List[T]] fails to infer constaints

  bugtopic-union-types
  python/mypy#11149 · Filter by author sobolevn opened on Sep 20, 2021
  2

• Mypy emits two conflicting results for reveal_type

  bugtopic-reveal-typetopic-union-types
  python/mypy#10739 · Filter by author akaptur opened on Jun 29, 2021
  4

• MyPy fails on Union[str, int] < Union[str, int] when underlying type is known

  bugtopic-type-narrowingtopic-union-types
  python/mypy#10380 · Filter by author muggenhor opened on Apr 28, 2021
  4

• nested isinstances lose type information

  bugfalse-positivetopic-join-v-uniontopic-type-narrowingtopic-union-types
  python/mypy#10146 · Filter by author Akuli opened on Feb 27, 2021
  2

• Get rid of make_simplified_union() except in error messages

  bugperformancepriority-1-normalrefactoringtopic-union-types
  python/mypy#8624 · Filter by author ilevkivskyi opened on Apr 3, 2020
  2

• Type variables in Callables don't unify

  bugfalse-positivepriority-1-normaltopic-type-variablestopic-union-types
  python/mypy#8275 · Filter by author maxrothman opened on Jan 11, 2020
  9

• TypedDict doesn't support Union[Literal] as key "string literal"

  bugpriority-2-lowtopic-literal-typestopic-typed-dicttopic-union-types
  python/mypy#7752 · Filter by author b0g3r opened on Oct 19, 2019
  2

• Union subtyping doesn't work with covariant type constructors Tuple and Callable

  bugfalse-positivepriority-0-hightopic-union-types
  python/mypy#7187 · Filter by author ilevkivskyi opened on Jul 9, 2019
  6

• "multiple values for keyword argument" with star expansion

  bugfalse-positivepriority-1-normaltopic-union-types
  python/mypy#6799 · Filter by author Eugeny opened on May 8, 2019
  11

• Can't infer T where Optional[T] is Optional[MyUnion]

  bugfalse-positivepriority-1-normaltopic-type-variablestopic-union-types
  python/mypy#6751 · Filter by author ghost opened on May 1, 2019
  5

• Same variable with a union type is not checked in "lockstep" within an expression

  false-positivefeaturepriority-2-lowtopic-union-types
  python/mypy#6478 · Filter by author Hanaasagi opened on Feb 25, 2019
  4

• Generics is not supported with some operators

  bugpriority-1-normaltopic-type-variablestopic-union-types
  python/mypy#6157 · Filter by author appraveen opened on Jan 7, 2019
  1

• Union types for dict keys are not inferred in union context

  bugfalse-positiveneeds discussionpriority-1-normaltopic-join-v-uniontopic-union-types
  python/mypy#6079 · Filter by author bryanforbes opened on Dec 17, 2018
  1

• Mypy is still too eager about outer context

  bugfalse-positivepriority-1-normaltopic-type-variablestopic-union-types
  python/mypy#5874 · Filter by author ilevkivskyi opened on Nov 8, 2018
  3