input: Write a Python function to retrieve the year, month, and day from a URL using regular expressions.
  assert retrieve_date("https://www.washingtonpost.com/news/football-insider/wp/2016/09/02/odell-beckhams-fame-rests-on-one-stupid-little-ball-josh-norman-tells-author/") == [('2016', '09', '02')]
  assert retrieve_date("https://www.indiatoday.in/movies/celebrities/story/wp/2020/11/03/odeof-sushant-singh-rajput-s-death-his-brother-in-law-shares-advice-for-fans-1749646/") == [('2020', '11', '03')]
  assert retrieve_date("https://economictimes.indiatimes.com/news/economy/2020/12/29/finance/pension-assets-under-pfrda-touch-rs-5-32-lakh-crore/articleshow/79736619.cms") == [('2020', '12', '29')]
output: def retrieve_date(url):
      import re
      return re.findall(r'/(\d{4})/(\d{2})/(\d{2})/', url)