improve syntaxerror message <> typo

Author: Aniketsy

Grammar/python.gram

@@ -801,8 +801,11 @@ compare_op_bitwise_or_pair[CmpopExprPair*]:
     | in_bitwise_or
     | isnot_bitwise_or
     | is_bitwise_or
+    | invalid_diamond_op
     | invalid_eqeqeq
 
+invalid_diamond_op:
+    | a='<' b='>' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '!=' instead of '<>'?") }
 eq_bitwise_or[CmpopExprPair*]: '==' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Eq, a) }
 invalid_eqeqeq:
     | a='==' b='=' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '==' instead of '==='?") }

Lib/test/test_syntax.py

@@ -3505,6 +3505,16 @@ def test_ifexp_body_stmt_else_stmt(self):
         ]:
             self._check_error(f"x = {lhs_stmt} if 1 else {rhs_stmt}", msg)
 
+    def test_diamond_operator(self):
+        self._check_error(
+            "1 < > 2",
+            "Maybe you meant '!=' instead of '<>'?",
+            lineno=1,
+            end_lineno=1,
+            offset=3,
+            end_offset=6,
+        )
+
     def test_triple_equal(self):
         self._check_error(
             "a === b",