indico/util/signals.py

   1 # This file is part of Indico.
   2 # Copyright (C) 2002 - 2015 European Organization for Nuclear Research (CERN).
   3 #
   4 # Indico is free software; you can redistribute it and/or
   5 # modify it under the terms of the GNU General Public License as
   6 # published by the Free Software Foundation; either version 3 of the
   7 # License, or (at your option) any later version.
   8 #
   9 # Indico is distributed in the hope that it will be useful, but
  10 # WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 # General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU General Public License
  15 # along with Indico; if not, see <http://www.gnu.org/licenses/>.
  16
  17 from itertools import izip_longest
  18 from types import GeneratorType
  19
  20
  21 def values_from_signal(signal_response, single_value=False, skip_none=True, as_list=False,
  22                        multi_value_types=GeneratorType, return_plugins=False):
  23     """Combines the results from both single-value and multi-value signals.
  24
  25     The signal needs to return either a single object (which is not a
  26     generator) or a generator (usually by returning its values using
  27     `yield`).
  28
  29     :param signal_response: The return value of a Signal's `.send()` method
  30     :param single_value: If each return value should be treated as a single
  31                          value in all cases (disables the generator check)
  32     :param skip_none: If None return values should be skipped
  33     :param as_list: If you want a list instead of a set (only use this if
  34                     you need non-hashable return values, the order is still
  35                     not defined!)
  36     :param multi_value_types: Types which should be considered multi-value.
  37                               It is used in an `isinstance()` call and if
  38                               the check succeeds, the value is passed to
  39                               `list.extend()`
  40     :param return_plugins: return `(plugin, value)` tuples instead of just
  41                            the values. `plugin` can be `None` if the signal
  42                            was not registered in a plugin.
  43     :return: A set/list containing the results
  44     """
  45     values = []
  46     for func, value in signal_response:
  47         plugin = getattr(func, 'indico_plugin', None)
  48         if not single_value and isinstance(value, multi_value_types):
  49             values.extend(izip_longest([plugin], value, fillvalue=plugin))
  50         else:
  51             values.append((plugin, value))
  52     if skip_none:
  53         values = [(p, v) for p, v in values if v is not None]
  54     if not return_plugins:
  55         values = [v for p, v in values]
  56     return values if as_list else set(values)
  57
  58
  59 def named_objects_from_signal(signal_response, name_attr='name', plugin_attr=None):
  60     """Returns a dict of objects based on an unique attribute on each object.
  61
  62     The signal needs to return either a single object (which is not a
  63     generator) or a generator (usually by returning its values using
  64     `yield`).
  65
  66     :param signal_response: The return value of a Signal's `.send()` method
  67     :param name_attr: The attribute containing each object's unique name
  68     :param plugin_attr: The attribute that will be set to the plugin containing
  69                         the object (set to `None` for objects in the core)
  70     :return: dict mapping object names to objects
  71     """
  72     objects = values_from_signal(signal_response, return_plugins=True)
  73     mapping = {getattr(cls, name_attr): cls for _, cls in objects}
  74     if plugin_attr is not None:
  75         for plugin, cls in objects:
  76             setattr(mapping[getattr(cls, name_attr)], plugin_attr, plugin)
  77     conflicting = {cls for _, cls in objects} - set(mapping.viewvalues())
  78     if conflicting:
  79         names = ', '.join(sorted(getattr(x, name_attr) for x in conflicting))
  80         raise RuntimeError('Non-unique object names: {}'.format(names))
  81     return mapping