cache calculated "next expiration" time

src/Cache.py

@@ -4,6 +4,8 @@ class Cache(object):
     def __init__(self):
         self._items = {}
 
+        self._cached_expiration = None
+
     def cache_key(self, key: str):
         return "sha1:%s" % hashlib.sha1(key.encode("utf8")).hexdigest()
 
@@ -15,17 +17,24 @@ class Cache(object):
     def _cache(self, key: str, value: typing.Any,
             expiration: typing.Optional[float]) -> str:
         id = self.cache_key(key)
+        self._cached_expiration = None
         self._items[id] = [key, value, expiration]
         return id
 
     def next_expiration(self) -> typing.Optional[float]:
+        if not self._cached_expiration == None:
+            return self._cached_expiration
+
         expirations = [value[-1] for value in self._items.values()]
         expirations = list(filter(None, expirations))
         if not expirations:
             return None
         now = time.monotonic()
         expirations = [e-now for e in expirations]
-        return max(min(expirations), 0)
+
+        expiration = max(min(expirations), 0)
+        self._cached_expiration = expiration
+        return expiration
 
     def expire(self):
         now = time.monotonic()
@@ -35,6 +44,7 @@ class Cache(object):
             if expiration and expiration <= now:
                 expired.append(id)
         for id in expired:
+            self._cached_expiration = None
             del self._items[id]
 
     def has_item(self, key: typing.Any) -> bool:
@@ -44,6 +54,7 @@ class Cache(object):
         key, value, expiration = self._items[self.cache_key(key)]
         return value
     def remove(self, key: str):
+        self._cached_expiration = None
         del self._items[self.cache_key(key)]
 
     def get_expiration(self, key: typing.Any) -> float: