gh-146495: Improve SyntaxError message for && and || operators

Lib/test/test_syntax.py

@@ -3505,6 +3505,26 @@ def test_ifexp_body_stmt_else_stmt(self):
         ]:
             self._check_error(f"x = {lhs_stmt} if 1 else {rhs_stmt}", msg)
 
+    def test_double_ampersand(self):
+        self._check_error(
+            "a && b",
+            "Maybe you meant 'and' or '&' instead of '&&'",
+            lineno=1,
+            end_lineno=1,
+            offset=3,
+            end_offset=5,
+        )
+
+    def test_double_pipe(self):
+        self._check_error(
+            "a || b",
+            "Maybe you meant 'or' or '|' 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/2026-06-04-15-02-35.gh-issue-146495.wWRRvx.rst

@@ -0,0 +1 @@
+Improve SyntaxError message for ``&&`` and ``||`` operators, suggesting ``and``/``&`` and ``or``/``|`` respectively.

Parser/pegen_errors.c

@@ -442,6 +442,16 @@
         RAISE_INDENTATION_ERROR(last_token->type == INDENT ? "unexpected indent" : "unexpected unindent");
         return;
     }
+    if (last_token->type == AMPER && p->tokens[p->fill - 2]->type == AMPER) {
+        RAISE_SYNTAX_ERROR_KNOWN_RANGE(p->tokens[p->fill - 2], last_token,
+                                       "invalid syntax.  Maybe you meant 'and' or '&' instead of '&&'");
+        return;
+    }
+    if (last_token->type == VBAR && p->tokens[p->fill - 2]->type == VBAR) {
+        RAISE_SYNTAX_ERROR_KNOWN_RANGE(p->tokens[p->fill - 2], last_token,
+                                       "invalid syntax.  Maybe you meant 'or' or '|' instead of '||'");
+        return;
+    }
     // Unknown error (generic case)
 
     // Use the last token we found on the first pass to avoid reporting