def METHOD_NAME(self, alias):
    """
    Retrieve the Matrix Room ID from the given alias (after adding the
    leading '#' and the Server name if not provided) and initialize the
    room_alias and room_id properties.
    :param alias:
    """
    if not alias:
        raise Exception("Matrix Room Alias not defined")
    # Add leading '#' if needed
    if alias[0] != '#':
        alias = '#' + alias
    # If the alias does not include the Server, add the domain
    if ':' not in alias:
        alias += ':' + self.domain
    self.room_alias = alias
    # Retrieve Room ID
    url = self.url('directory/room/') + urllib.parse.quote(alias)
    r = requests.get(url, headers=self._headers)
    if r.status_code != requests.codes.ok:
        raise Exception(r.json()['error'])
    self.room_id = r.json()['room_id']