add aurweb.cache, a redis caching utility module

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/cache.py

@@ -0,0 +1,20 @@
+from redis import Redis
+from sqlalchemy import orm
+
+
+async def db_count_cache(redis: Redis, key: str, query: orm.Query,
+                         expire: int = None) -> int:
+    """ Store and retrieve a query.count() via redis cache.
+
+    :param redis: Redis handle
+    :param key: Redis key
+    :param query: SQLAlchemy ORM query
+    :param expire: Optional expiration in seconds
+    :return: query.count()
+    """
+    result = redis.get(key)
+    if result is None:
+        redis.set(key, (result := int(query.count())))
+        if expire:
+            redis.expire(key, expire)
+    return int(result)