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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 _machine_check_connectivity():
 """ This method calls to docker-machine on the command line and makes sure that it is up and ready. Potential improvements to be made: - Support multiple machine names (run a `docker-machine ls` and then see which machines are active. Use a priority list) """

    with open(devnull, 'w') as devnull_f:
        try:
            status = subprocess.check_output(
                ['docker-machine', 'status', 'dev'],
                stderr=devnull_f).strip()
            if status == 'Stopped':
                raise DatacatsError('Please start your docker-machine '
                                    'VM with "docker-machine start dev"')

            # XXX HACK: This exists because of
            #           http://github.com/datacats/datacats/issues/63,
            # as a temporary fix.
            if 'tls' in _docker_kwargs:
                # It will print out messages to the user otherwise.
                _docker_kwargs['tls'].assert_hostname = False
        except subprocess.CalledProcessError:
            raise DatacatsError('Please create a docker-machine with '
                                '"docker-machine start dev"')