Add type hints to DictionaryCache and TTLCache. (#9442)

synapse/util/caches/ttlcache.py

@@ -15,6 +15,7 @@
 
 import logging
 import time
+from typing import Any, Callable, Dict, Generic, Tuple, TypeVar, Union
 
 import attr
 from sortedcontainers import SortedList
@@ -23,15 +24,19 @@ from synapse.util.caches import register_cache
 
 logger = logging.getLogger(__name__)
 
-SENTINEL = object()
+SENTINEL = object()  # type: Any
+
+T = TypeVar("T")
+KT = TypeVar("KT")
+VT = TypeVar("VT")
 
 
-class TTLCache:
+class TTLCache(Generic[KT, VT]):
     """A key/value cache implementation where each entry has its own TTL"""
 
-    def __init__(self, cache_name, timer=time.time):
+    def __init__(self, cache_name: str, timer: Callable[[], float] = time.time):
         # map from key to _CacheEntry
-        self._data = {}
+        self._data = {}  # type: Dict[KT, _CacheEntry]
 
         # the _CacheEntries, sorted by expiry time
         self._expiry_list = SortedList()  # type: SortedList[_CacheEntry]
@@ -40,26 +45,27 @@ class TTLCache:
 
         self._metrics = register_cache("ttl", cache_name, self, resizable=False)
 
-    def set(self, key, value, ttl):
+    def set(self, key: KT, value: VT, ttl: float) -> None:
         """Add/update an entry in the cache
 
         Args:
             key: key for this entry
             value: value for this entry
-            ttl (float): TTL for this entry, in seconds
+            ttl: TTL for this entry, in seconds
         """
         expiry = self._timer() + ttl
 
         self.expire()
         e = self._data.pop(key, SENTINEL)
-        if e != SENTINEL:
+        if e is not SENTINEL:
+            assert isinstance(e, _CacheEntry)
             self._expiry_list.remove(e)
 
         entry = _CacheEntry(expiry_time=expiry, ttl=ttl, key=key, value=value)
         self._data[key] = entry
         self._expiry_list.add(entry)
 
-    def get(self, key, default=SENTINEL):
+    def get(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:
         """Get a value from the cache
 
         Args:
@@ -72,23 +78,23 @@ class TTLCache:
         """
         self.expire()
         e = self._data.get(key, SENTINEL)
-        if e == SENTINEL:
+        if e is SENTINEL:
             self._metrics.inc_misses()
-            if default == SENTINEL:
+            if default is SENTINEL:
                 raise KeyError(key)
             return default
+        assert isinstance(e, _CacheEntry)
         self._metrics.inc_hits()
         return e.value
 
-    def get_with_expiry(self, key):
+    def get_with_expiry(self, key: KT) -> Tuple[VT, float, float]:
         """Get a value, and its expiry time, from the cache
 
         Args:
             key: key to look up
 
         Returns:
-            Tuple[Any, float, float]: the value from the cache, the expiry time
-            and the TTL
+            A tuple of  the value from the cache, the expiry time and the TTL
 
         Raises:
             KeyError if the entry is not found
@@ -102,7 +108,7 @@ class TTLCache:
         self._metrics.inc_hits()
         return e.value, e.expiry_time, e.ttl
 
-    def pop(self, key, default=SENTINEL):
+    def pop(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:  # type: ignore
         """Remove a value from the cache
 
         If key is in the cache, remove it and return its value, else return default.
@@ -118,29 +124,30 @@ class TTLCache:
         """
         self.expire()
         e = self._data.pop(key, SENTINEL)
-        if e == SENTINEL:
+        if e is SENTINEL:
             self._metrics.inc_misses()
-            if default == SENTINEL:
+            if default is SENTINEL:
                 raise KeyError(key)
             return default
+        assert isinstance(e, _CacheEntry)
         self._expiry_list.remove(e)
         self._metrics.inc_hits()
         return e.value
 
-    def __getitem__(self, key):
+    def __getitem__(self, key: KT) -> VT:
         return self.get(key)
 
-    def __delitem__(self, key):
+    def __delitem__(self, key: KT) -> None:
         self.pop(key)
 
-    def __contains__(self, key):
+    def __contains__(self, key: KT) -> bool:
         return key in self._data
 
-    def __len__(self):
+    def __len__(self) -> int:
         self.expire()
         return len(self._data)
 
-    def expire(self):
+    def expire(self) -> None:
         """Run the expiry on the cache. Any entries whose expiry times are due will
         be removed
         """
@@ -158,7 +165,7 @@ class _CacheEntry:
     """TTLCache entry"""
 
     # expiry_time is the first attribute, so that entries are sorted by expiry.
-    expiry_time = attr.ib()
-    ttl = attr.ib()
+    expiry_time = attr.ib(type=float)
+    ttl = attr.ib(type=float)
     key = attr.ib()
     value = attr.ib()