initial import for Open Source 🎉

util/expiresdict.py

@@ -0,0 +1,84 @@
+from datetime import datetime
+
+from six import iteritems
+
+
+class ExpiresEntry(object):
+  """ A single entry under a ExpiresDict. """
+  def __init__(self, value, expires=None):
+    self.value = value
+    self._expiration = expires
+
+  @property
+  def expired(self):
+    if self._expiration is None:
+      return False
+
+    return datetime.now() >= self._expiration
+
+
+class ExpiresDict(object):
+  """ ExpiresDict defines a dictionary-like class whose keys have expiration. The rebuilder is
+      a function that returns the full contents of the cached dictionary as a dict of the keys
+      and whose values are TTLEntry's. If the rebuilder is None, then no rebuilding is performed.
+  """
+  def __init__(self, rebuilder=None):
+    self._rebuilder = rebuilder
+    self._items = {}
+
+  def __getitem__(self, key):
+    found = self.get(key)
+    if found is None:
+      raise KeyError
+
+    return found
+
+  def get(self, key, default_value=None):
+    # Check the cache first. If the key is found and it has not yet expired,
+    # return it.
+    found = self._items.get(key)
+    if found is not None and not found.expired:
+      return found.value
+
+    # Otherwise the key has expired or was not found. Rebuild the cache and check it again.
+    items = self._rebuild()
+    found_item = items.get(key)
+    if found_item is None:
+      return default_value
+
+    return found_item.value
+
+  def __contains__(self, key):
+    return self.get(key) is not None
+
+  def _rebuild(self):
+    if self._rebuilder is None:
+      return self._items
+
+    items = self._rebuilder()
+    self._items = items
+    return items
+
+  def _alive_items(self):
+    return {k: entry.value for (k, entry) in self._items.items() if not entry.expired}
+
+  def items(self):
+    return self._alive_items().items()
+
+  def iteritems(self):
+    return iteritems(self._alive_items())
+
+  def __iter__(self):
+    return iter(self._alive_items())
+
+  def __delitem__(self, key):
+    del self._items[key]
+
+  def __len__(self):
+    return len(self._alive_items())
+
+  def set(self, key, value, expires=None):
+    self._items[key] = ExpiresEntry(value, expires=expires)
+
+  def __setitem__(self, key, value):
+    return self.set(key, value)