def openapi_keyname(key):
    """
    Returns the OpenAPI name for keys.

    :param key:
    :type key: str
    :return: OpenAPI name for `key`
    :rtype str
    """
    _key = {'_in': 'in', '_not': 'not', '_ref': '$ref', '_type': 'type',
        '_format': 'format', '_license': 'license', 'dollar_ref': '$ref',
        'all_of': 'allOf', 'any_of': 'anyOf', 'one_of': 'oneOf',
        'max_items': 'maxItems', 'min_items': 'minItems', 'read_only':
        'readOnly', 'max_length': 'maxLength', 'min_length': 'minLength',
        'write_only': 'writeOnly', 'multiple_of': 'multipleOf',
        'operation_id': 'operationId', 'request_body': 'requestBody',
        'unique_items': 'uniqueItems', 'external_docs': 'externalDocs',
        'property_name': 'propertyName', 'max_properties': 'maxProperties',
        'min_properties': 'minProperties', 'terms_of_service':
        'termsOfService', 'security_schemes': 'securitySchemes',
        'exclusive_maximum': 'exclusiveMaximum', 'exclusive_minimum':
        'exclusiveMinimum', 'additional_properties': 'additionalProperties'
        }.get(key, key)
    return _key
