gh-151303 : Improve SyntaxError suggestions for common operator typos and cross-language mistakes

Grammar/python.gram

@@ -802,6 +802,7 @@ compare_op_bitwise_or_pair[CmpopExprPair*]:
     | in_bitwise_or
     | isnot_bitwise_or
     | is_bitwise_or
+    | invalid_eqeqeq
 
 eq_bitwise_or[CmpopExprPair*]: '==' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Eq, a) }
 noteq_bitwise_or[CmpopExprPair*]:
@@ -1316,6 +1317,21 @@ invalid_assignment:
             "'%s' is an illegal expression for augmented assignment",
             _PyPegen_get_expr_name(a)
         )}
+    | star_expressions a='=' b='<' {
+        _PyPegen_tokens_are_adjacent(a, b)
+        ? RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '<=' instead of '=<'?")
+        : NULL
+    }
+    | star_expressions a='=' b='>' {
+        _PyPegen_tokens_are_adjacent(a, b)
+        ? RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '>=' instead of '=>'?")
+        : NULL
+    }
+    | star_expressions a='=' b='!' {
+        _PyPegen_tokens_are_adjacent(a, b)
+        ? RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '!=' instead of '=!'?")
+        : NULL
+    }
 invalid_ann_assign_target[expr_ty]:
     | list
     | tuple
@@ -1660,3 +1676,10 @@ invalid_bitwise_or:
         ? RAISE_SYNTAX_ERROR_KNOWN_RANGE(b, c, "invalid syntax.  Maybe you meant 'or' or '|' instead of '||'?")
         : NULL
     }
+
+invalid_eqeqeq:
+    | a='==' b='=' {
+        _PyPegen_tokens_are_adjacent(a, b)
+        ? RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '==' instead of '==='?")
+        : NULL
+    }

Lib/test/test_syntax.py

@@ -3634,6 +3634,34 @@ def test_double_ampersand(self):
             end_offset=6,
         )
 
+    def test_triple_equal(self):
+        self._check_error(
+            "a === b",
+            r"Maybe you meant '==' instead of '==='\?",
+            lineno=1,
+            end_lineno=1,
+            offset=3,
+            end_offset=6,
+        )
+        self._check_error(
+            "a == = b",
+            "invalid syntax",
+            lineno=1,
+            end_lineno=1,
+            offset=6,
+            end_offset=7,
+        )
+
+    def test_eq_lt_typo(self):
+        self._check_error(
+            "a =< b",
+            r"Maybe you meant '<=' instead of '=<'\?",
+            lineno=1,
+            end_lineno=1,
+            offset=3,
+            end_offset=5,
+        )
+
     def test_double_pipe(self):
         self._check_error(
             "a || b",
@@ -3652,6 +3680,26 @@ def test_double_pipe(self):
             end_offset=6,
         )
 
+    def test_eq_gt_typo(self):
+        self._check_error(
+            "a => b",
+            r"Maybe you meant '>=' instead of '=>'\?",
+            lineno=1,
+            end_lineno=1,
+            offset=3,
+            end_offset=5,
+        )
+
+    def test_eq_bang_typo(self):
+        self._check_error(
+            "a =! b",
+            r"Maybe you meant '!=' instead of '=!'\?",
+            lineno=1,
+            end_lineno=1,
+            offset=3,
+            end_offset=5,
+        )
+
 
 class LazyImportRestrictionTestCase(SyntaxErrorTestCase):
     """Test syntax restrictions for lazy imports."""

Misc/NEWS.d/next/Core_and_Builtins/2026-06-12-03-41-39.gh-issue-151303.mzlJxi.rst

@@ -0,0 +1 @@
+Improve :exc:`SyntaxError` messages for common operator typos coming from other languages: ``=<``, ``=>``, and ``=!`` now suggest ``<=``, ``>=``, and ``!=`` respectively, and ``===`` suggests ``==``.