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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_assigned_licenses(service_instance, entity_ref=None, entity_name=None,
                          license_assignment_manager=None):
    '''
    Returns the licenses assigned to an entity. If entity ref is not provided,
    then entity_name is assumed to be the vcenter. This is later checked if
    the entity name is provided.

    service_instance
        The Service Instance Object from which to obtain the licenses.

    entity_ref
        VMware entity to get the assigned licenses for.
        If None, the entity is the vCenter itself.
        Default is None.

    entity_name
        Entity name used in logging.
        Default is None.

    license_assignment_manager
        The LicenseAssignmentManager object of the service instance.
        If not provided it will be retrieved.
        Default is None.
    '''
    if not license_assignment_manager:
        license_assignment_manager = \
                get_license_assignment_manager(service_instance)
    if not entity_name:
        raise salt.exceptions.ArgumentValueError('No entity_name passed')
    # If entity_ref is not defined, then interested in the vcenter
    entity_id = None
    entity_type = 'moid'
    check_name = False
    if not entity_ref:
        if entity_name:
            check_name = True
        entity_type = 'uuid'
        try:
            entity_id = service_instance.content.about.instanceUuid
        except vim.fault.NoPermission as exc:
            log.exception(exc)
            raise salt.exceptions.VMwareApiError(
                'Not enough permissions. Required privilege: '
                '{0}'.format(exc.privilegeId))
        except vim.fault.VimFault as exc:
            log.exception(exc)
            raise salt.exceptions.VMwareApiError(exc.msg)
        except vmodl.RuntimeFault as exc:
            log.exception(exc)
            raise salt.exceptions.VMwareRuntimeError(exc.msg)
    else:
        entity_id = entity_ref._moId

    log.trace('Retrieving licenses assigned to \'%s\'', entity_name)
    try:
        assignments = \
                license_assignment_manager.QueryAssignedLicenses(entity_id)
    except vim.fault.NoPermission as exc:
        log.exception(exc)
        raise salt.exceptions.VMwareApiError(
            'Not enough permissions. Required privilege: '
            '{0}'.format(exc.privilegeId))
    except vim.fault.VimFault as exc:
        log.exception(exc)
        raise salt.exceptions.VMwareApiError(exc.msg)
    except vmodl.RuntimeFault as exc:
        log.exception(exc)
        raise salt.exceptions.VMwareRuntimeError(exc.msg)

    if entity_type == 'uuid' and len(assignments) > 1:
        log.trace('Unexpectectedly retrieved more than one'
                  ' VCenter license assignment.')
        raise salt.exceptions.VMwareObjectRetrievalError(
            'Unexpected return. Expect only a single assignment')

    if check_name:
        if entity_name != assignments[0].entityDisplayName:
            log.trace('Getting license info for wrong vcenter: %s != %s',
                      entity_name, assignments[0].entityDisplayName)
            raise salt.exceptions.VMwareObjectRetrievalError(
                'Got license assignment info for a different vcenter')

    return [a.assignedLicense for a in assignments]