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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(self, parallel=True, debug=False, force=False, machine_readable=False):
 """Executes a `packer build` :param bool parallel: Run builders in parallel :param bool debug: Run in debug mode :param bool force: Force artifact output even if exists :param bool machine_readable: Make output machine-readable """

        self.packer_cmd = self.packer.build

        self._add_opt('-parallel=true' if parallel else None)
        self._add_opt('-debug' if debug else None)
        self._add_opt('-force' if force else None)
        self._add_opt('-machine-readable' if machine_readable else None)
        self._append_base_arguments()
        self._add_opt(self.packerfile)

        return self.packer_cmd()