input: from typing import Set
  
  def crawl(url: str) -> Set[str]:
      """
      Create a web crawler in Python that starts from a given website and looks for other links in the page then scrapes the page content.
      The crawler should keep track of the visited URLs and return the set of all visited URLs.
      >>> crawl('http://example.com')
      {'http://example.com', 'http://example.com/about', 'http://example.com/contact'}
      """
output:     import requests
      from bs4 import BeautifulSoup
      from urllib.parse import urljoin
  
      visited_urls = set()
      to_visit = [url]
  
      while to_visit:
          current_url = to_visit.pop(0)
          if current_url in visited_urls:
              continue
  
          try:
              response = requests.get(current_url)
              response.raise_for_status()
          except requests.RequestException:
              continue
  
          visited_urls.add(current_url)
  
          soup = BeautifulSoup(response.text, 'html.parser')
          for link in soup.find_all('a', href=True):
              absolute_url = urljoin(current_url, link['href'])
              if absolute_url not in visited_urls:
                  to_visit.append(absolute_url)
  
      return visited_urls