def open(self, *a, **k):
        """
        Override 'open' to track all files opened by this path.
        """
        f = filepath.FilePath.open(self, *a, **k)
        self.openedFiles.append(f)
        return f

        Override 'open' to track all files opened by this path.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_paths.py