code: def get_user(prompt=None):
      
      # Read username and password.
      try:
          env_user = getpass.getuser()
      except KeyError:
          env_user = ''
      if prompt is None:
          prompt = "Please enter your user name"
      if env_user is None or env_user == '':
          user = input('%s: ' % prompt)
      else:
          user = input('%s [%s]: ' % (prompt, env_user))
          if user == '':
              user = env_user
      return user
docs: Prompts the user for his login name, defaulting to the USER environment
      variable. Returns a string containing the username.
      May throw an exception if EOF is given by the user.
  
      :type  prompt: str|None
      :param prompt: The user prompt or the default one if None.
      :rtype:  string
      :return: A username.