def ExpandWindowsUserEnvironmentVariables(data_string,
                                          knowledge_base,
                                          sid=None,
                                          username=None):
  r"""Take a string and expand windows user environment variables based.

  Args:
    data_string: A string, e.g. "%TEMP%\\LogFiles"
    knowledge_base: A knowledgebase object.
    sid: A Windows SID for a user to expand for.
    username: A Windows user name to expand for.

  Returns:
    A string with available environment variables expanded.
  """
  win_environ_regex = re.compile(r"%([^%]+?)%")
  components = []
  offset = 0
  for match in win_environ_regex.finditer(data_string):
    components.append(data_string[offset:match.start()])
    kb_user = knowledge_base.GetUser(sid=sid, username=username)
    kb_value = None
    if kb_user:
      kb_value = getattr(kb_user, match.group(1).lower(), None)
    if isinstance(kb_value, string_types) and kb_value:
      components.append(kb_value)
    else:
      components.append("%%%s%%" % match.group(1))
    offset = match.end()

  components.append(data_string[offset:])  # Append the final chunk.
  return "".join(components)
r"""Take a string and expand windows user environment variables based.

  Args:
    data_string: A string, e.g. "%TEMP%\\LogFiles"
    knowledge_base: A knowledgebase object.
    sid: A Windows SID for a user to expand for.
    username: A Windows user name to expand for.

  Returns:
    A string with available environment variables expanded.