no f-string here because of backward compatibility

Author: Xiaozhou Li

Charon/filetypes/OpenPackagingConvention.py

@@ -299,7 +299,7 @@ def _processAliases(self, virtual_path: str) -> str:
         # Replace all aliases.
         for regex, replacement in self._aliases.items():
             if regex.startswith("/"):
-                expression = rf"^{regex}"
+                expression = r"^" + regex
             else:
                 expression = regex
             virtual_path = re.sub(expression, replacement, virtual_path)