src/pyqt/gui/adapt.py

   1 class AdaptationError(TypeError):
   2         pass
   3 class LiskovViolation(AdaptationError):
   4         pass
   5
   6 _adapter_factory_registry = {}
   7
   8 def registerAdapterFactory(objtype, protocol, factory):
   9         _adapter_factory_registry[objtype, protocol] = factory
  10
  11 def unregisterAdapterFactory(objtype, protocol):
  12         del _adapter_factory_registry[objtype, protocol]
  13
  14 def _adapt_by_registry(obj, protocol, alternate):
  15         factory = _adapter_factory_registry.get((type(obj), protocol))
  16         if factory is None:
  17             adapter = alternate
  18         else:
  19             adapter = factory(obj, protocol, alternate)
  20         if adapter is AdaptationError:
  21             raise AdaptationError,obj
  22         else:
  23             return adapter
  24
  25
  26 def adapt(obj, protocol, alternate=AdaptationError):
  27
  28         t = type(obj)
  29
  30         # (a) first check to see if object has the exact protocol
  31         if t is protocol:
  32            return obj
  33
  34         try:
  35             # (b) next check if t.__conform__ exists & likes protocol
  36             conform = getattr(t, '__conform__', None)
  37             if conform is not None:
  38                 result = conform(obj, protocol)
  39                 if result is not None:
  40                     return result
  41
  42             # (c) then check if protocol.__adapt__ exists & likes obj
  43             adapt = getattr(type(protocol), '__adapt__', None)
  44             if adapt is not None:
  45                 result = adapt(protocol, obj)
  46                 if result is not None:
  47                     return result
  48         except LiskovViolation:
  49             pass
  50         else:
  51             # (d) check if object is instance of protocol
  52             try:
  53                if isinstance(obj, protocol):
  54                    return obj
  55             except:
  56                pass
  57
  58         # (e) last chance: try the registry
  59         return _adapt_by_registry(obj, protocol, alternate)