Source code for openpathsampling.netcdfplus.proxy


@author: JH Prinz
import functools
import weakref

from .base import StorableObject
from six import exec_

# =============================================================================
# Loader Proxy
# =============================================================================

[docs]class LoaderProxy(object): """ A proxy that loads an underlying object if attributes are accessed """ __slots__ = ['_subject', '__uuid__', '_store', '__weakref__'] # add a global stash to remember existing Proxy objects _stash = weakref.WeakValueDictionary() @classmethod def new(cls, store, uid): obj = LoaderProxy._stash.get(uid) if obj is not None: return obj else: obj = cls(store, uid) LoaderProxy._stash[uid] = obj return obj
[docs] def __init__(self, store, uid): self.__uuid__ = uid self._store = store self._subject = None
@property def __subject__(self): if self._subject is not None: obj = self._subject() if obj is not None: return obj ref = self._load_() if ref is None: return None self._subject = weakref.ref(ref) return ref @property def reversed(self): return, StorableObject.ruuid(self.__uuid__)) @property def _reversed(self): return, StorableObject.ruuid(self.__uuid__)) def __eq__(self, other): if self is other: return True if hasattr(other, '__uuid__'): return self.__uuid__ == other.__uuid__ return NotImplemented def __getitem__(self, item): return self.__subject__[item] def __ne__(self, other): return not self == other def __hash__(self): return self.__uuid__ & 1152921504606846975 def __len__(self): return len(self.__subject__) @property def __class__(self): return self._store.content_class def __getattr__(self, item): return getattr(self.__subject__, item) def _load_(self): """ Call the loader and get the referenced object """ try: return self._store.load(self.__uuid__) except KeyError: if type(self.__uuid__) is int: raise RuntimeWarning( 'Index %s is not in store. This should never happen!' % self._idx) else: raise RuntimeWarning( 'Object %s is not in store. Attach it using fallbacks.' % self._idx)
[docs]class DelayedLoader(object): """ Descriptor class to handle proxy objects in attributes If a proxy is stored in an attribute then the full object will be returned """ def __get__(self, instance, owner): if instance is not None: obj = instance._lazy[self] if hasattr(obj, '_idx'): return obj.__subject__ else: return obj else: return self def __set__(self, instance, value): instance._lazy[self] = value
[docs]def lazy_loading_attributes(*attributes): """ Set attributes in the decorated class to be handled as lazy loaded objects. An attribute that is added here will be turned into a special descriptor that will dynamically load an objects if it is represented internally as a LoaderProxy object and will return the real object, not the proxy! The second thing you can do is that saving using the `.write()` command will automatically remove the real object and turn the stored object into a proxy Notes ----- This decorator will obfuscate the __init__ signature in Python 2. This is fixed in Python 3.4+ Examples -------- Set an attribute to a LoaderProxy >>> my_obj.lazy_attribute = LoaderProxy(snapshot_store, 13) >>> print my_obj.lazy_attribute openpathsampling.Snapshot object It will not return the proxy. This is completely hidden. If you want to use the intelligent saving that will remove the reference to the object you can do >>> sample_store.write('parent', index, my_sample) After this call the attribute `my_sample.parent` will be turned into a proxy """ def _decorator(cls): for attr in attributes: setattr(cls, attr, DelayedLoader()) _super_init = cls.__init__ code = 'def _init(self, %s):' source_code = '\n'.join(code) cc = compile(source_code, '<string>', 'exec') #exec cc in locals() exec_(cc, locals()) @functools.wraps(cls.__init__) def _init(self, *args, **kwargs): self._lazy = {} _super_init(self, *args, **kwargs) cls.__init__ = _init return cls return _decorator