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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 load_ext(self):
 """Read the internal data from an external data file."""

        try:
            sequencemanager = hydpy.pub.sequencemanager
        except AttributeError:
            raise RuntimeError(
                'The time series of sequence %s cannot be loaded.  Firstly, '
                'you have to prepare `pub.sequencemanager` correctly.'
                % objecttools.devicephrase(self))
        sequencemanager.load_file(self)