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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 open_files(self, idx=0):
 """Call method |Devices.open_files| of the |Nodes| and |Elements| objects currently handled by the |HydPy| object."""

        self.elements.open_files(idx=idx)
        self.nodes.open_files(idx=idx)