def _header_to_id(self, header):
    """Convert a Content-ID header value to an id.

    Presumes the Content-ID header conforms to the format that _id_to_header()
    returns.

    Args:
      header: string, Content-ID header value.

    Returns:
      The extracted id value.

    Raises:
      BatchError if the header is not in the expected format.
    """
    if header[0] != '<' or header[-1] != '>':
      raise BatchError("Invalid value for Content-ID: %s" % header)
    if header not in '+':
      raise BatchError("Invalid value for Content-ID: %s" % header)
    base, id_ = header[1:-1].rsplit('+', 1)

    return urllib.unquote(id_)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/google-api-python-client/apiclient/http.py/BatchHttpRequest._header_to_id/swapped operands of `not in`