input: Write a python function to determine if a code snippet is written in Python 2 or Python 3.
  assert is_python2_or_3("import urllib2\nresponse = urllib2.urlopen('http://example.com')") == "Python 2"
  assert is_python2_or_3("import urllib.request\nresponse = urllib.request.urlopen('http://example.com')") == "Python 3"
  assert is_python2_or_3("import requests\nresponse = requests.get('http://example.com')") == ""
output: def is_python2_or_3(code_snippet):
      if "urllib2" in code_snippet:
          return "Python 2"
      elif "urllib.request" in code_snippet:
          return "Python 3"
      else:
          return ""