Find last of a series of linking tweets

import sys
from lxml.etree import HTMLParser, fromstring
from lxml.cssselect import CSSSelector
import requests

url = sys.argv[1]
counter = 1

while True:
    tweet = requests.get(url)
    doc = fromstring(tweet.content, HTMLParser())

    contents_selector = CSSSelector('.tweet-text')
    contents = contents_selector(doc)
    if not contents:
            break

    text = contents[0].text
    url_selector = CSSSelector('.twitter-timeline-link')
    url = url_selector(doc)[0].attrib['title']

    print("%d: %s %s" % (counter, text, url))
    counter += 1