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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _file_lines(self, filename):
 """Get lines for filename, caching opened files."""

        try:
            return self._file_lines_cache[filename]
        except KeyError:
            if os.path.isfile(filename):
                with open(filename) as python_file:
                    self._file_lines_cache[filename] = python_file.readlines()
            else:
                self._file_lines_cache[filename] = ""

            return self._file_lines_cache[filename]