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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 create_diskgroup(cache_disk_id, capacity_disk_ids, safety_checks=True,
                     service_instance=None):
    '''
    Creates disk group on an ESXi host with the specified cache and
    capacity disks.

    cache_disk_id
        The canonical name of the disk to be used as a cache. The disk must be
        ssd.

    capacity_disk_ids
        A list containing canonical names of the capacity disks. Must contain at
        least one id. Default is True.

    safety_checks
        Specify whether to perform safety check or to skip the checks and try
        performing the required task. Default value is True.

    service_instance
        Service instance (vim.ServiceInstance) of the vCenter/ESXi host.
        Default is None.

    .. code-block:: bash

        salt '*' vsphere.create_diskgroup cache_disk_id='naa.000000000000001'
            capacity_disk_ids='[naa.000000000000002, naa.000000000000003]'
    '''
    log.trace('Validating diskgroup input')
    schema = DiskGroupsDiskIdSchema.serialize()
    try:
        jsonschema.validate(
            {'diskgroups': [{'cache_id': cache_disk_id,
                              'capacity_ids': capacity_disk_ids}]},
            schema)
    except jsonschema.exceptions.ValidationError as exc:
        raise ArgumentValueError(exc)
    host_ref = _get_proxy_target(service_instance)
    hostname = __proxy__['esxi.get_details']()['esxi_host']
    if safety_checks:
        diskgroups = \
                salt.utils.vmware.get_diskgroups(host_ref, [cache_disk_id])
        if diskgroups:
            raise VMwareObjectExistsError(
                'Diskgroup with cache disk id \'{0}\' already exists ESXi '
                'host \'{1}\''.format(cache_disk_id, hostname))
    disk_ids = capacity_disk_ids[:]
    disk_ids.insert(0, cache_disk_id)
    disks = salt.utils.vmware.get_disks(host_ref, disk_ids=disk_ids)
    for id in disk_ids:
        if not [d for d in disks if d.canonicalName == id]:
            raise VMwareObjectRetrievalError(
                'No disk with id \'{0}\' was found in ESXi host \'{1}\''
                ''.format(id, hostname))
    cache_disk = [d for d in disks if d.canonicalName == cache_disk_id][0]
    capacity_disks = [d for d in disks if d.canonicalName in capacity_disk_ids]
    vsan_disk_mgmt_system = \
            salt.utils.vsan.get_vsan_disk_management_system(service_instance)
    dg = salt.utils.vsan.create_diskgroup(service_instance,
                                          vsan_disk_mgmt_system,
                                          host_ref,
                                          cache_disk,
                                          capacity_disks)
    return True