input: Write a function to crawl a website for a specific type of data and return the extracted data. The function should take the website URL and the type of data to crawl as inputs. If the data to crawl is phone numbers, it should extract all phone numbers in the format 'ddd-ddd-dddd' from the website's content. If the data to crawl is not specified, the function should return an empty list.
  
  
  import requests
  import re
  
  def crawl_website(website, data_to_crawl):
      if data_to_crawl == 'phone numbers':
          response = requests.get(website)
          phone_numbers = re.findall('\d{3}-\d{3}-\d{4}', response.text)
          return phone_numbers
      else:
          return []
  
  if __name__ == '__main__':
      print(crawl_website('www.example.com', 'phone numbers'))
  
  
  assert crawl_website('www.example.com', 'phone numbers') == ['123-456-7890', '987-654-3210']
  assert crawl_website('www.example.com', 'email addresses') == []
  assert crawl_website('www.example.com', 'postal codes') == []
  assert crawl_website('www.example.com', '') == []
  assert crawl_website('', 'phone numbers') == []
output: import requests
  import re
  
  def crawl_website(website, data_to_crawl):
      if data_to_crawl == 'phone numbers':
          response = requests.get(website)
          phone_numbers = re.findall('\d{3}-\d{3}-\d{4}', response.text)
          return phone_numbers
      else:
          return []