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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 _build_master(cls):
 """ Prepare the master working set. """

        ws = cls()
        try:
            from __main__ import __requires__
        except ImportError:
            # The main program does not list any requirements
            return ws

        # ensure the requirements are met
        try:
            ws.require(__requires__)
        except VersionConflict:
            return cls._build_from_requirements(__requires__)

        return ws