fix: use unambiguous punction in 'invalid escape sequence' message (GH-26582)

Author: nedbat

Lib/test/test_cmd_line_script.py

@@ -651,7 +651,7 @@ def test_syntaxerror_invalid_escape_sequence_multi_line(self):
                 stderr.splitlines()[-3:],
                 [   b'    foo = """\\q"""',
                     b'          ^^^^^^^^',
-                    b'SyntaxError: invalid escape sequence \\q'
+                    b'SyntaxError: invalid escape sequence \'\\q\''
                 ],
             )
 

Parser/string_parser.c

@@ -12,7 +12,7 @@ static int
 warn_invalid_escape_sequence(Parser *p, unsigned char first_invalid_escape_char, Token *t)
 {
     PyObject *msg =
-        PyUnicode_FromFormat("invalid escape sequence \\%c", first_invalid_escape_char);
+        PyUnicode_FromFormat("invalid escape sequence '\\%c'", first_invalid_escape_char);
     if (msg == NULL) {
         return -1;
     }
@@ -27,7 +27,7 @@ warn_invalid_escape_sequence(Parser *p, unsigned char first_invalid_escape_char,
                since _PyPegen_raise_error uses p->tokens[p->fill - 1] for the
                error location, if p->known_err_token is not set. */
             p->known_err_token = t;
-            RAISE_SYNTAX_ERROR("invalid escape sequence \\%c", first_invalid_escape_char);
+            RAISE_SYNTAX_ERROR("invalid escape sequence '\\%c'", first_invalid_escape_char);
         }
         Py_DECREF(msg);
         return -1;