manifold/util/functional.py

   1 """Borrowed from Django."""
   2
   3 from threading import Lock
   4
   5 class LazyObject(object):
   6     """
   7     A wrapper for another class that can be used to delay instantiation of the
   8     wrapped class.
   9
  10     By subclassing, you have the opportunity to intercept and alter the
  11     instantiation. If you don't need to do that, use SimpleLazyObject.
  12     """
  13     def __init__(self):
  14         self._wrapped = None
  15         self._lock = Lock()
  16
  17     def __getattr__(self, name):
  18         self._lock.acquire()
  19         if self._wrapped is None:
  20             self._setup()
  21         self._lock.release()
  22         return getattr(self._wrapped, name)
  23
  24     def __setattr__(self, name, value):
  25         if name in ["_wrapped", "_lock"]:
  26             # Assign to __dict__ to avoid infinite __setattr__ loops.
  27             self.__dict__[name] = value
  28         else:
  29             if self._wrapped is None:
  30                 self._setup()
  31             setattr(self._wrapped, name, value)
  32
  33     def __delattr__(self, name):
  34         if name == "_wrapped":
  35             raise TypeError("can't delete _wrapped.")
  36         if self._wrapped is None:
  37             self._setup()
  38         delattr(self._wrapped, name)
  39
  40     def _setup(self):
  41         """
  42         Must be implemented by subclasses to initialise the wrapped object.
  43         """
  44         raise NotImplementedError
  45
  46     # introspection support:
  47     __members__ = property(lambda self: self.__dir__())
  48
  49     def __dir__(self):
  50         if self._wrapped is None:
  51             self._setup()
  52         return  dir(self._wrapped)
  53