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 getattr(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 __repr__(self):
  43         return "LazyUUIDTask: {0}".format(self._uuid)
  44
  45     @property
  46     def saved(self):
  47         """
  48         Implementation of the 'saved' property. Always returns True.
  49         """
  50         return True
  51
  52     def replace(self):
  53         """
  54         Performs conversion to the regular Task object, referenced by the
  55         stored UUID.
  56         """
  57
  58         replacement = self._tw.tasks.get(uuid=self._uuid)
  59         self.__class__ = replacement.__class__
  60         self.__dict__ = replacement.__dict__
  61
  62
  63 class LazyUUIDTaskSet(object):
  64     """
  65     A lazy wrapper around TaskQuerySet object, for tasks referenced by UUID.
  66
  67     - Supports 'in' operator with LazyUUIDTask or Task objects
  68     - If iteration over the objects in the LazyUUIDTaskSet is requested, the
  69       LazyUUIDTaskSet will be converted to QuerySet and evaluated
  70     """
  71
  72     def __init__(self, tw, uuids):
  73         self._tw = tw
  74         self._uuids = set(uuids)
  75
  76     def __getattr__(self, name):
  77         # Getattr is called only if the attribute could not be found using
  78         # normal means
  79
  80         if name.startswith('__'):
  81             # If some internal method was being search, do not convert
  82             # to TaskQuerySet just because of that
  83             raise AttributeError
  84         else:
  85             self.replace()
  86             return getattr(self, name)
  87
  88     def __repr__(self):
  89         return "LazyUUIDTaskSet([{0}])".format(', '.join(self._uuids))
  90
  91     def __eq__(self, other):
  92         return set(t['uuid'] for t in other) == self._uuids
  93
  94     def __ne__(self, other):
  95         return not (self == other)
  96
  97     def __contains__(self, task):
  98         return task['uuid'] in self._uuids
  99
 100     def __len__(self):
 101         return len(self._uuids)
 102
 103     def __iter__(self):
 104         for uuid in self._uuids:
 105             yield LazyUUIDTask(self._tw, uuid)
 106
 107     def __sub__(self, other):
 108         return LazyUUIDTaskSet(self._tw,
 109                                self._uuids - set(t['uuid'] for t in other))
 110
 111     def __isub__(self, other):
 112         self._uuids -= set(t['uuid'] for t in other)
 113         return self
 114
 115     def __or__(self, other):
 116         return LazyUUIDTaskSet(self._tw,
 117                                self._uuids | set(t['uuid'] for t in other))
 118
 119     def __ior__(self, other):
 120         self._uuids |= set(t['uuid'] for t in other)
 121         return self
 122
 123     def replace(self):
 124         """
 125         Performs conversion to the regular TaskQuerySet object, referenced by
 126         the stored UUIDs.
 127         """
 128
 129         replacement = self._tw.tasks.filter(' '.join(self._uuids))
 130         self.__class__ = replacement.__class__
 131         self.__dict__ = replacement.__dict__