src/mailman/utilities/queries.py

   1 # Copyright (C) 2016 by the Free Software Foundation, Inc.
   2 #
   3 # This file is part of GNU Mailman.
   4 #
   5 # GNU Mailman is free software: you can redistribute it and/or modify it under
   6 # the terms of the GNU General Public License as published by the Free
   7 # Software Foundation, either version 3 of the License, or (at your option)
   8 # any later version.
   9 #
  10 # GNU Mailman is distributed in the hope that it will be useful, but WITHOUT
  11 # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12 # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  13 # more details.
  14 #
  15 # You should have received a copy of the GNU General Public License along with
  16 # GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
  17
  18 """Some helpers for queries."""
  19
  20 __all__ = [
  21     'QuerySequence',
  22     ]
  23
  24
  25 from collections.abc import Sequence
  26
  27
  28 class QuerySequence(Sequence):
  29     def __init__(self, query=None):
  30         super().__init__()
  31         self._query = query
  32         self._cached_results = None
  33
  34     def __len__(self):
  35         return (0 if self._query is None else self._query.count())
  36
  37     def __getitem__(self, index):
  38         if self._query is None:
  39             raise IndexError('index out of range')
  40         if self._cached_results is None:
  41             self._cached_results = list(self._query)
  42         return self._cached_results[index]