Oct 19, 2025 · Oct 17, 2025 · Oct 17, 2025
diff --git a/mypy/checker.py b/mypy/checker.py
        """
        if isinstance(s, AssertStmt) and is_false_literal(s.expr):
            return True
        elif isinstance(s, ReturnStmt) and is_literal_not_implemented(s.expr):
            return True
        elif isinstance(s, (RaiseStmt, PassStmt)):
            return True
        elif isinstance(s, ExpressionStmt):
    return isinstance(n, NameExpr) and n.fullname == "builtins.None"


 def is_literal_not_implemented(n: Expression) -> bool:
 def is_literal_not_implemented(n: Expression | None) -> bool:
    return isinstance(n, NameExpr) and n.fullname == "builtins.NotImplemented"


diff --git a/test-data/unit/check-unreachable-code.test b/test-data/unit/check-unreachable-code.test
 reveal_type(foo().attr)  # N: Revealed type is "Never"
 1  # E: Statement is unreachable

 [case testIgnoreReturningNotImplemented]
 # flags: --warn-unreachable

 class C:
    def __add__(self, o: C) -> C:
        if not isinstance(o, C):
            return NotImplemented
        return C()
    def __sub__(self, o: C) -> C:
        if isinstance(o, C):
            return C()
        return NotImplemented
    def __mul__(self, o: C) -> C:
        if isinstance(o, C):
            return C()
        else:
            return NotImplemented

 [builtins fixtures/isinstance.pyi]

 [case testUnreachableStatementPrettyHighlighting]
 # flags: --warn-unreachable --pretty
 def x() -> None:
Original file line number	Diff line number	Diff line change
Expand Up		@@ -3147,6 +3147,8 @@ def is_noop_for_reachability(self, s: Statement) -> bool:
		"""
		if isinstance(s, AssertStmt) and is_false_literal(s.expr):
		return True
		elif isinstance(s, ReturnStmt) and is_literal_not_implemented(s.expr):
		return True
		elif isinstance(s, (RaiseStmt, PassStmt)):
		return True
		elif isinstance(s, ExpressionStmt):
Expand DownExpand Up		@@ -8281,7 +8283,7 @@ def is_literal_none(n: Expression) -> bool:
		return isinstance(n, NameExpr) and n.fullname == "builtins.None"


		def is_literal_not_implemented(n: Expression) -> bool:
		def is_literal_not_implemented(n: Expression \| None) -> bool:
		return isinstance(n, NameExpr) and n.fullname == "builtins.NotImplemented"


Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1620,6 +1620,26 @@ reveal_type(bar().attr) # N: Revealed type is "Never"
		reveal_type(foo().attr) # N: Revealed type is "Never"
		1 # E: Statement is unreachable

		[case testIgnoreReturningNotImplemented]
		# flags: --warn-unreachable

		class C:
		def __add__(self, o: C) -> C:
		if not isinstance(o, C):
		return NotImplemented
		return C()
		def __sub__(self, o: C) -> C:
		if isinstance(o, C):
		return C()
		return NotImplemented
		def __mul__(self, o: C) -> C:
		if isinstance(o, C):
		return C()
		else:
		return NotImplemented

		[builtins fixtures/isinstance.pyi]

		[case testUnreachableStatementPrettyHighlighting]
		# flags: --warn-unreachable --pretty
		def x() -> None:
Expand Down