input: Write a function to crawl a given website for specific data, in this case, phone numbers. The function should return a list of phone numbers found on the website. If the website is empty or cannot be accessed, return an empty list. The phone number format is expected as '###-###-####'.
  
  assert crawl_website_for_phone_numbers('www.example.com')==['123-456-7890', '987-654-3210']
  assert crawl_website_for_phone_numbers('www.emptywebsite.com')==[]
  assert crawl_website_for_phone_numbers('www.nonexistentwebsite.com')==[]
output: import re
  import requests
  
  def crawl_website_for_phone_numbers(url):
      try:
          response = requests.get(f"http://{url}")
          response.raise_for_status()
          content = response.text
          phone_numbers = re.findall(r'\b\d{3}-\d{3}-\d{4}\b', content)
          return phone_numbers
      except:
          return []