|
|
class _Missing(object):
|
|
|
|
|
|
def __repr__(self):
|
|
|
return 'no value'
|
|
|
|
|
|
def __reduce__(self):
|
|
|
return '_missing'
|
|
|
|
|
|
_missing = _Missing()
|
|
|
|
|
|
|
|
|
class LazyProperty(object):
|
|
|
"""
|
|
|
Decorator for easier creation of ``property`` from potentially expensive to
|
|
|
calculate attribute of the class.
|
|
|
|
|
|
Usage::
|
|
|
|
|
|
class Foo(object):
|
|
|
@LazyProperty
|
|
|
def bar(self):
|
|
|
print 'Calculating self._bar'
|
|
|
return 42
|
|
|
|
|
|
Taken from http://blog.pythonisito.com/2008/08/lazy-descriptors.html and
|
|
|
used widely.
|
|
|
"""
|
|
|
|
|
|
def __init__(self, func):
|
|
|
self._func = func
|
|
|
self.__module__ = func.__module__
|
|
|
self.__name__ = func.__name__
|
|
|
self.__doc__ = func.__doc__
|
|
|
|
|
|
def __get__(self, obj, klass=None):
|
|
|
if obj is None:
|
|
|
return self
|
|
|
value = obj.__dict__.get(self.__name__, _missing)
|
|
|
if value is _missing:
|
|
|
value = self._func(obj)
|
|
|
obj.__dict__[self.__name__] = value
|
|
|
return value
|
|
|
|
|
|
import threading
|
|
|
|
|
|
|
|
|
class ThreadLocalLazyProperty(LazyProperty):
|
|
|
"""
|
|
|
Same as above but uses thread local dict for cache storage.
|
|
|
"""
|
|
|
|
|
|
def __get__(self, obj, klass=None):
|
|
|
if obj is None:
|
|
|
return self
|
|
|
if not hasattr(obj, '__tl_dict__'):
|
|
|
obj.__tl_dict__ = threading.local().__dict__
|
|
|
|
|
|
value = obj.__tl_dict__.get(self.__name__, _missing)
|
|
|
if value is _missing:
|
|
|
value = self._func(obj)
|
|
|
obj.__tl_dict__[self.__name__] = value
|
|
|
return value
|
|
|
|
