def clean_node(node):
    """Split and normalize a node name from an ismaster response."""
    host, port = partition_node(node)

    # Normalize hostname to lowercase, since DNS is case-insensitive:
    # http://tools.ietf.org/html/rfc4343
    # This prevents useless rediscovery if "foo.com" is in the seed list but
    # "FOO.com" is in the ismaster response.
    return host.lower(), port
Split and normalize a node name from an ismaster response.
stackoverflow/venv/lib/python3.6/site-packages/pymongo/common.py