input: 
  def extract_urls(url: str) -> list:
      """Extracts all URLs from a given webpage using BeautifulSoup.
      >>> extract_urls("https://example.com")
      ['https://example.com/page1', 'https://example.com/page2']
      >>> extract_urls("https://another-example.com")
      ['https://another-example.com/another-page']
      """
      import requests
      from bs4 import BeautifulSoup
  
      webpage = requests.get(url)
      soup = BeautifulSoup(webpage.content, 'html.parser')
      links = soup.find_all('a')
      urls = [link.get('href') for link in links]
      return urls
  
output:     filtered_urls = []
      for u in urls:
          if u and u.startswith('http'):
              filtered_urls.append(u)
      return filtered_urls