Release 577b0566ea

__init__.py

                 * **keys():** returns a list of all available keys.
                 * **data_version():** returns a version number of the current data (it should be increased, if the get method of the source instance returns improved values or the data structure had been changed).
                 * **get(key, default):** returns the property for a key. If key does not exists, default will be returned.
-    
+
     :param source_instance: The source instance holding the data
     :type source_instance: instance
     :param cache_filename: File name, where the properties are stored as cache
     #
     STORAGE_VERSION = 1
 
-    def __init__(self, source_instance, cache_filename, load_all_on_init=False, callback_on_data_storage=None, max_age=None, store_on_get=True):
+    def __init__(self, source_instance, cache_filename, load_all_on_init=False, callback_on_data_storage=None, max_age=None, store_on_get=True, return_source_on_none=False):
         self._source_instance = source_instance
         self._cache_filename = cache_filename
         self._load_all_on_init = load_all_on_init
         self._callback_on_data_storage = callback_on_data_storage
         self._max_age = max_age
         self._store_on_get = store_on_get
+        self._return_source_on_none = return_source_on_none
         #
         self._source_get_keys = []
         self._cached_props = None
                     return val
             else:
                 logger.debug("Providing property for '%s' from cache", key)
-            return self._cached_props[self.DATA_TAG].get(self._key_filter(key), default)
+            cached_data = self._cached_props[self.DATA_TAG].get(self._key_filter(key), default)
+            if cached_data is None and self._return_source_on_none:
+                return self._source_instance.get(key, default)
+            return cached_data
         else:
             if key not in self._source_instance.keys():
                 logger.debug("Key '%s' is not in cached_keys. Uncached data will be returned.", key)
-            elif key in self._source_get_keys:
+            else:
                 logger.debug("Key '%s' is excluded by .add_source_get_keys(). Uncached data will be returned.", key)
             return self._source_instance.get(key, default)
 
             self._cached_props[self.UID_TAG] = self._source_instance.uid()
             self._cached_props[self.DATA_VERSION_TAG] = self._source_instance.data_version()
             self._cached_props[self.STORAGE_VERSION_TAG] = self.STORAGE_VERSION
-            if self._store_on_get:
-                self._save_cache()
+
+    def _load_only(self):
+        with open(self._cache_filename, 'rb') as fh:
+            self._cached_props = pickle.load(fh)
+        logger.debug('Loading properties from cache (%s)', self._cache_filename)
 
     def _load_cache(self):
         if os.path.exists(self._cache_filename):
-            with open(self._cache_filename, 'rb') as fh:
-                self._cached_props = pickle.load(fh)
-            logger.debug('Loading properties from cache (%s)', self._cache_filename)
+            self._load_only()
             return True
         else:
             logger.debug('Cache file does not exists (yet).')
                 self._cached_props[self.AGE_TAG][self._key_filter(key)] = int(time.time())
                 time.sleep(sleep_between_keys)
 
-    def _save_cache(self):
+    def _save_only(self):
         with open(self._cache_filename, 'wb') as fh:
             pickle.dump(self._cached_props, fh)
             logger.debug('cache-file stored (%s)', self._cache_filename)
+
+    def _save_cache(self):
+        self._save_only()
         if self._callback_on_data_storage is not None:
             self._callback_on_data_storage(self)
 
 
     .. literalinclude:: caching/_examples_/property_cache_json_2.log
     """
-    def _load_cache(self):
-        if os.path.exists(self._cache_filename):
-            with open(self._cache_filename, 'r') as fh:
-                self._cached_props = json.load(fh)
-            logger.debug('Loading properties from cache (%s)', self._cache_filename)
-            return True
-        else:
-            logger.debug('Cache file does not exists (yet).')
-        return False
 
-    def _save_cache(self):
+    def _load_only(self):
+        with open(self._cache_filename, 'r') as fh:
+            self._cached_props = json.load(fh)
+        logger.debug('Loading properties from cache (%s)', self._cache_filename)
+
+    def _save_only(self):
         with open(self._cache_filename, 'w') as fh:
             json.dump(self._cached_props, fh, sort_keys=True, indent=4)
             logger.debug('cache-file stored (%s)', self._cache_filename)
-        if self._callback_on_data_storage is not None:
-            self._callback_on_data_storage(self)