input: Write a function to extract links from a given website using the urllib and re modules.
  assert extract_links('http://www.example.com/') == ['http://www.example.com/link1', 'http://www.example.com/link2']
  assert extract_links('http://www.testsite.com/') == ['http://www.testsite.com/home', 'http://www.testsite.com/about']
  assert extract_links('http://www.anotherexample.com/') == ['http://www.anotherexample.com/page1', 'http://www.anotherexample.com/page2']
output: import urllib.request
  import re
  
  def extract_links(url):
      response = urllib.request.urlopen(url)
      html = response.read().decode('utf-8')
      links = re.findall(r'href="(http[s]?://[^"]+)"', html)
      return links