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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 _attach_subcommands(self):
 """Create a subparser and add the registered commands to it. This will also call ``_init`` on each subcommand (in turn invoking its ``_attach_subcommands`` method). """

        if self.subcommands:
            self.subparsers = self.parser.add_subparsers()

            for subcommand in self.subcommands:
                subparser = self.subparsers.add_parser(subcommand.name,
                                                       help=subcommand.title)
                if subcommand.handler:
                    self._register_handler(subparser, subcommand.handler)
                subcommand._init(subparser)