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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 halt(self, vm_name=None, force=False):
        '''
        Halt the Vagrant box.

        force: If True, force shut down.
        '''
        force_opt = '--force' if force else None
        self._call_vagrant_command(['halt', vm_name, force_opt])
        self._cached_conf[vm_name] = None