improved comments

Author: randolf-scholz

mypy/checkexpr.py

@@ -4049,18 +4049,19 @@ def lookup_definer(typ: Instance, attr_name: str) -> str | None:
 
             variants_raw = [(op_name, left_op, left_type, right_expr)]
         elif (
-            # Note: use covers_at_runtime instead of is_subtype.
-            #    fixes https://github.com/python/mypy/issues/19006
+            # Note: use `covers_at_runtime` instead of `is_subtype` (#19006)
             covers_at_runtime(right_type, left_type)
             and (
+                # Checking (A implies B) using the logically equivalent (not A or B), where
+                #    A: left and right are both `Instance` objects
+                #    B: right's __rop__ method is different from left's __op__ method
                 not (isinstance(left_type, Instance) and isinstance(right_type, Instance))
                 or (
-                    (
+                    lookup_definer(left_type, op_name) != lookup_definer(right_type, rev_op_name)
+                    and (
                         left_type.type.alt_promote is None
                         or left_type.type.alt_promote.type is not right_type.type
                     )
-                    and lookup_definer(left_type, op_name)
-                    != lookup_definer(right_type, rev_op_name)
                 )
             )
         ):

test-data/unit/check-expressions.test

@@ -681,8 +681,8 @@ class B:
 s: str
 s = A() + B() # E: Unsupported operand types for + ("A" and "B")
 
-[case testReverseBinaryOperator4]
 
+[case testReverseBinaryOperator4]
 from typing import assert_type, Never
 
 class Size(tuple[int, ...]):