def _get_k8s_model_attribute(model_type, field_name):
    """
    Takes a model type and a Kubernetes API resource field name (such as
    "serviceAccount") and returns a related attribute name (such as
    "service_account") to be used with  kubernetes.client.models objects. It is
    impossible to prove a negative but it seems like it is always a question of
    making camelCase to snake_case but by using the provided 'attribute_map' we
    also ensure that the fields actually exist.

    Example of V1PodSpec's attribute_map:
    {
        'active_deadline_seconds': 'activeDeadlineSeconds',
        'affinity': 'affinity',
        'automount_service_account_token': 'automountServiceAccountToken',
        'containers': 'containers',
        'dns_policy': 'dnsPolicy',
        'host_aliases': 'hostAliases',
        'host_ipc': 'hostIPC',
        'host_network': 'hostNetwork',
        'host_pid': 'hostPID',
        'hostname': 'hostname',
        'image_pull_secrets': 'imagePullSecrets',
        'init_containers': 'initContainers',
        'node_name': 'nodeName',
        'node_selector': 'nodeSelector',
        'priority': 'priority',
        'priority_class_name': 'priorityClassName',
        'restart_policy': 'restartPolicy',
        'scheduler_name': 'schedulerName',
        'security_context': 'securityContext',
        'service_account': 'serviceAccount',
        'service_account_name': 'serviceAccountName',
        'subdomain': 'subdomain',
        'termination_grace_period_seconds': 'terminationGracePeriodSeconds',
        'tolerations': 'tolerations',
        'volumes': 'volumes'
    }
    """
    if field_name in model_type.attribute_map:
        return field_name
    for key, value in model_type.attribute_map.items():
        if value == field_name:
            return key
    else:
        raise ValueError("'{}' did not have an attribute matching '{}'".
            format(model_type.__name__, field_name))
