input: Write a python function to fetch the contents of a web page using the given URL.
  assert fetch_webpage('http://example.com/index.html')[:15] == b'<!doctype html>'
  assert fetch_webpage('http://example.com')[:15] == b'<!doctype html>'
  assert fetch_webpage('http://example.com/nonexistent') == b''
output: def fetch_webpage(url):
      import requests
      try:
          response = requests.get(url)
          response.raise_for_status()  # Raise an error for bad status codes
          return response.content
      except (requests.exceptions.HTTPError, requests.exceptions.RequestException):
          return b''