def check_in_lambda():
    """
    Return None if SDK is not loaded in AWS Lambda worker.
    Otherwise drop a touch file and return a lambda context.
    """
    if not os.getenv(LAMBDA_TASK_ROOT_KEY):
        return None

    try:
        os.mkdir(TOUCH_FILE_DIR)
    except OSError:
        log.debug('directory %s already exists', TOUCH_FILE_DIR)

    try:
        f = open(TOUCH_FILE_PATH, 'w+')
        f.close()
        # utime force second parameter in python2.7
        os.utime(TOUCH_FILE_PATH, None)
    except (IOError, OSError):
        log.warning("Unable to write to %s. Failed to signal SDK initialization." % TOUCH_FILE_PATH)

    return LambdaContext()
Return None if SDK is not loaded in AWS Lambda worker.
    Otherwise drop a touch file and return a lambda context.