def _maybe_parse_container(self):
    """Try to parse a container type (dict, list, or tuple)."""
    bracket_types = {
        '{': ('}', dict, self._parse_dict_item),
        '(': (')', tuple, self.parse_value),
        '[': (']', list, self.parse_value)
    }
    if self._current_token.value in bracket_types:
      open_bracket = self._current_token.value
      close_bracket, type_fn, parse_item = bracket_types[open_bracket]
      self._advance()

      values = []
      saw_comma = False
      while self._current_token.value != close_bracket:
        values.append(parse_item())
        if self._current_token.value == ',':
          saw_comma = True
          self._advance()
        elif self._current_token.value != close_bracket:
          self._raise_syntax_error("Expected ',' or '%s'." % close_bracket)

      # If it's just a single value enclosed in parentheses without a trailing
      # comma, it's not a tuple, so just grab the value.
      if type_fn is tuple and len(values) == 1 and not saw_comma:
        type_fn = lambda x: x[0]

      self._advance()
      return True, type_fn(values)

    return False, None
Try to parse a container type (dict, list, or tuple).