py, lexer: Fix parsing of raw strings (allow escaping of quote).

py/lexer.c

@@ -455,9 +455,13 @@ STATIC void mp_lexer_next_token_into(mp_lexer_t *lex, mp_token_t *tok, bool firs
                 vstr_add_char(&lex->vstr, CUR_CHAR(lex));
             } else {
                 n_closing = 0;
-                if (!is_raw && is_char(lex, '\\')) {
+                if (is_char(lex, '\\')) {
                     next_char(lex);
                     unichar c = CUR_CHAR(lex);
+                    if (is_raw) {
+                        // raw strings allow escaping of quotes, but the backslash is also emitted
+                        vstr_add_char(&lex->vstr, '\\');
+                    } else {
                         switch (c) {
                             case MP_LEXER_CHAR_EOF: break; // TODO a proper error message?
                             case '\n': c = MP_LEXER_CHAR_EOF; break; // TODO check this works correctly (we are supposed to ignore it
@@ -500,6 +504,7 @@ STATIC void mp_lexer_next_token_into(mp_lexer_t *lex, mp_token_t *tok, bool firs
                                 }
                                 break;
                         }
+                    }
                     if (c != MP_LEXER_CHAR_EOF) {
                         vstr_add_char(&lex->vstr, c);
                     }