tasklib/lazy.py

   1 """
   2 Provides lazy implementations for Task and TaskQuerySet.
   3 """
   4
   5
   6 class LazyUUIDTask(object):
   7     """
   8     A lazy wrapper around Task object, referenced by UUID.
   9
  10     - Supports comparison with LazyUUIDTask or Task objects (equality by UUIDs)
  11     - If any attribute other than 'uuid' requested, a lookup in the
  12       backend will be performed and this object will be replaced by a proper
  13       Task object.
  14     """
  15
  16     def __init__(self, tw, uuid):
  17         self._tw = tw
  18         self._uuid = uuid
  19
  20     def __getitem__(self, key):
  21         # LazyUUIDTask does not provide anything else other than 'uuid'
  22         if key is 'uuid':
  23             return self._uuid
  24         else:
  25             self.replace()
  26             return self[key]
  27
  28     def __getattr__(self, name):
  29         # Getattr is called only if the attribute could not be found using
  30         # normal means
  31         self.replace()
  32         return self.name
  33
  34     def __eq__(self, other):
  35         if other['uuid']:
  36             # For saved Tasks, just define equality by equality of uuids
  37             return self['uuid'] == other['uuid']
  38
  39     def __hash__(self):
  40         return self['uuid'].__hash__()
  41
  42     def replace(self):
  43         """
  44         Performs conversion to the regular Task object, referenced by the
  45         stored UUID.
  46         """
  47
  48         replacement = self._tw.tasks.get(uuid=self._uuid)
  49         self.__class__ = replacement.__class__
  50         self.__dict__ = replacement.__dict__
  51
  52
  53 class LazyUUIDTaskSet(object):
  54     """
  55     A lazy wrapper around TaskQuerySet object, for tasks referenced by UUID.
  56
  57     - Supports 'in' operator with LazyUUIDTask or Task objects
  58     - If iteration over the objects in the LazyUUIDTaskSet is requested, the
  59       LazyUUIDTaskSet will be converted to QuerySet and evaluated
  60     """
  61
  62     def __init__(self, tw, uuids):
  63         self._tw = tw
  64         self._uuids = set(uuids)
  65
  66     def __getattr__(self, name):
  67         # Getattr is called only if the attribute could not be found using
  68         # normal means
  69
  70         if name.startswith('__'):
  71             # If some internal method was being search, do not convert
  72             # to TaskQuerySet just because of that
  73             raise AttributeError
  74         else:
  75             self.replace()
  76             return self.name
  77
  78     def __eq__(self, other):
  79         return set(t['uuid'] for t in other) == self._uuids
  80
  81     def __contains__(self, task):
  82         return task['uuid'] in self._uuids
  83
  84     def __len__(self):
  85         return len(self._uuids)
  86
  87     def __iter__(self):
  88         for uuid in self._uuids:
  89             yield LazyUUIDTask(self._tw, uuid)
  90
  91     def replace(self):
  92         """
  93         Performs conversion to the regular TaskQuerySet object, referenced by
  94         the stored UUIDs.
  95         """
  96
  97         replacement = self._tw.tasks.filter(' '.join(self._uuids))
  98         self.__class__ = replacement.__class__
  99         self.__dict__ = replacement.__dict__