def METHOD_NAME(
    service_name: str, operation_name: str, region: str, aws_request: AWSPreparedRequest
) -> RequestContext:
    context = RequestContext()
    context.service = load_service(service_name)
    context.operation = context.service.operation_model(operation_name=operation_name)
    context.region = region
    if hasattr(aws_request.body, "read"):
        aws_request.body = aws_request.body.read()
    context.request = create_http_request(aws_request)
    parser = create_parser(context.service)
    _, instance = parser.parse(context.request)
    context.service_request = instance
    context.account_id = get_account_id_from_request(context.request)
    return context