input: Write a python function to extract all hyperlink URLs from a given HTML string using BeautifulSoup.
  assert parseHtml('<html><head><title>Test</title></head><body><a href="http://example.com">example</a></body></html>') == ['http://example.com']
  assert parseHtml('<html><body><a href="http://example1.com">example1</a><a href="http://example2.com">example2</a></body></html>') == ['http://example1.com', 'http://example2.com']
  assert parseHtml('<html><body>No links here!</body></html>') == []
output: def parseHtml(html):
      from bs4 import BeautifulSoup
      
      soup = BeautifulSoup(html, 'html.parser')
      links = [a['href'] for a in soup.find_all('a', href=True)]
      return links