I am using simples3 version 1.0. When calling listdir on s3 key that has a lot more than 1000 files, the generator return only the first 1000 files.
The method has an optional limit argument which is None by default. Setting the limit return an empty list. And there is no additional limit to listdir mentioned in the documentation.
Here is a code example, where bucket is simples3 S3Bucket and s3_key is a key in s3 that include over 5000 files under it:
count = 0
for file_info in bucket.listdir(prefix=s3_key):
count += 1
1000 ## Expected to be over 5000