input: Write a python function to extract all links from a given URL using requests and BeautifulSoup.
  assert extract_links("https://www.example.com") == ['https://www.iana.org/domains/example']
  assert extract_links("https://httpbin.org/") == ['/forms/post', 'https://github.com/requests/httpbin', 'https://kennethreitz.org', 'https://twitter.com/intent/follow?screen_name=kenreitz42']
  assert extract_links("https://www.wikipedia.org/") == ['https://www.wikipedia.org/portal/wikipedia.org/assets/img/Wikipedia-logo-v2.png', '#', 'https://en.wikipedia.org/', 'https://de.wikipedia.org/', 'https://es.wikipedia.org/', 'https://fr.wikipedia.org/', 'https://it.wikipedia.org/', 'https://nl.wikipedia.org/', 'https://ja.wikipedia.org/', 'https://ru.wikipedia.org/', 'https://zh.wikipedia.org/', 'https://www.wikimediafoundation.org/', 'https://en.wikipedia.org/wiki/List_of_Wikipedias']
output: def extract_links(url):
      import requests
      from bs4 import BeautifulSoup
  
      response = requests.get(url)
      soup = BeautifulSoup(response.text, 'html.parser')
      links = [a.get('href') for a in soup.find_all('a', href=True)]
      return links