if __name__ == '__main__':
    client = boto3.client('s3', aws_access_key_id='access_key',
        aws_secret_access_key='secret_key')

def get_all_object_keys(bucket, prefix, start_after='', keys=[]):
    response = client.list_objects_v2(Bucket=bucket, Prefix=prefix,
        StartAfter=start_after)
if 'Contents' not in response:
    return keys
key_list = response['Contents']
last_key = key_list[-1]['Key']
keys.extend(key_list)
return get_all_object_keys(bucket, prefix, last_key, keys)
object_keys = get_all_object_keys('your_bucket', 'prefix/to/files')
Как узнать размер коллекции boto3?