How to use the cryptostore.engines.StorageEngines.boto3 function in cryptostore

def aws_write(bucket, key, data, creds=(None, None), endpoint=None):
    client = StorageEngines.boto3.client('s3',
        aws_access_key_id=creds[0],
        aws_secret_access_key=creds[1],
        endpoint_url=endpoint
    )

    with open(data, 'rb') as fp:
        client.upload_fileobj(fp, bucket, key)

def aws_list(bucket, key, creds=(None, None), limit=None, endpoint=None):
    client = StorageEngines.boto3.client('s3',
        aws_access_key_id=creds[0],
        aws_secret_access_key=creds[1],
        endpoint_url=endpoint
    )

    objs = client.list_objects_v2(Bucket=bucket, Prefix=key)
    if objs and 'Contents' in objs:
        ret = []
        if limit:
            for obj in objs['Contents']:
                ret.append(obj['Key'])
                limit -= 1
                if not limit:
                    break
            return ret
        else: