input: Write a function to generate a Python code for crawling a website for a specific type of data. The function should take the website URL and the type of data to crawl as inputs, and return the extracted data. The data to crawl in this case is phone numbers, which should be identified using a regular expression for phone numbers in the format 'xxx-xxx-xxxx'.
  
  def generate_crawling_code(website, data_type):
      if data_type == 'phone numbers':
          return f"""
  import requests
  import re
  
  def crawl_website_for_phone_numbers(website):
      response = requests.get(website)
      phone_numbers = re.findall('\\\\d{{3}}-\\\\d{{3}}-\\\\d{{4}}', response.text)
      return phone_numbers
      
  if __name__ == '__main__':
      print(crawl_website_for_phone_numbers('{website}'))
  """
      
      return "Unknown data type"
  
  assert generate_crawling_code('www.example.com', 'phone numbers') == """
  import requests
  import re
  
  def crawl_website_for_phone_numbers(website):
      response = requests.get(website)
      phone_numbers = re.findall('\\\\\\d{3}-\\\\d{3}-\\\\d{4}', response.text)
      return phone_numbers
      
  if __name__ == '__main__':
      print(crawl_website_for_phone_numbers('www.example.com'))
  """
  
  assert generate_crawling_code('www.example.com', 'email addresses') == "Unknown data type"
output: 
  def generate_crawling_code(website, data_type):
      if data_type == 'phone numbers':
          return f"""
  import requests
  import re
  
  def crawl_website_for_phone_numbers(website):
      response = requests.get(website)
      phone_numbers = re.findall('\\\\d{{3}}-\\\\d{{3}}-\\\\d{{4}}', response.text)
      return phone_numbers
      
  if __name__ == '__main__':
      print(crawl_website_for_phone_numbers('{website}'))
  """
      
      return "Unknown data type"
  