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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 _get_vsan_datastore(si, cluster_name):
    '''Retrieves the vsan_datastore'''

    log.trace('Retrieving vsan datastore')
    vsan_datastores = [ds for ds in
                       __salt__['vsphere.list_datastores_via_proxy'](
                           service_instance=si)
                       if ds['type'] == 'vsan']

    if not vsan_datastores:
        raise salt.exceptions.VMwareObjectRetrievalError(
            'No vSAN datastores where retrieved for cluster '
            '\'{0}\''.format(cluster_name))
    return vsan_datastores[0]