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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ensure_arg(args, arg, param=None):
 """Make sure the arg is present in the list of args. If arg is not present, adds the arg and the optional param. If present and param != None, sets the parameter following the arg to param. :param list args: strings representing an argument list. :param string arg: argument to make sure is present in the list. :param string param: parameter to add or update after arg in the list. :return: possibly modified list of args. """

  for idx, found_arg in enumerate(args):
    if found_arg == arg:
      if param is not None:
        args[idx + 1] = param
      return args

  args.append(arg)
  if param is not None:
    args.append(param)
  return args