Extending Mark's answer. AWS has also added support for a bucket.s3.aws-region.amazonaws.com/key1/key2 URL pattern (. instead of -).

This is also the Object URL given on the S3 bucket file's page.

So, the 2nd regex pattern can be updated with a [-.], to capture a single - or . character, allowing it to match against both bucket.s3-aws-region.amazonaws.com/key1/key2 & bucket.s3.aws-region.amazonaws.com/key1/key2.

    match =  re.search('^https?://(.+).s3[-.]([^.]+).amazonaws.com/', url)
    if match:
        return match.group(1), match.group(2)

Reference: https://docs.aws.amazon.com/AmazonS3/latest/userguide/VirtualHosting.html#VirtualHostingBackwardsCompatibility mentions bucket.s3-aws-region.amazonaws.com (- instead of . seperating s3 & aws-region) is the legacy endpoint and recommends using this new pattern.

( P.S. I don't have enough reputation to add a comment to Mark's answer, hence have posted this as a new answer )