1 files changed, 52 insertions, 0 deletions
diff --git a/src/cachetools/keys.py b/src/cachetools/keys.py
new file mode 100644
index 0000000..13630a4
--- /dev/null
+++ b/src/cachetools/keys.py
@@ -0,0 +1,52 @@
+"""Key functions for memoizing decorators."""
+
+__all__ = ("hashkey", "typedkey")
+
+
+class _HashedTuple(tuple):
+    """A tuple that ensures that hash() will be called no more than once
+    per element, since cache decorators will hash the key multiple
+    times on a cache miss.  See also _HashedSeq in the standard
+    library functools implementation.
+
+    """
+
+    __hashvalue = None
+
+    def __hash__(self, hash=tuple.__hash__):
+        hashvalue = self.__hashvalue
+        if hashvalue is None:
+            self.__hashvalue = hashvalue = hash(self)
+        return hashvalue
+
+    def __add__(self, other, add=tuple.__add__):
+        return _HashedTuple(add(self, other))
+
+    def __radd__(self, other, add=tuple.__add__):
+        return _HashedTuple(add(other, self))
+
+    def __getstate__(self):
+        return {}
+
+
+# used for separating keyword arguments; we do not use an object
+# instance here so identity is preserved when pickling/unpickling
+_kwmark = (_HashedTuple,)
+
+
+def hashkey(*args, **kwargs):
+    """Return a cache key for the specified hashable arguments."""
+
+    if kwargs:
+        return _HashedTuple(args + sum(sorted(kwargs.items()), _kwmark))
+    else:
+        return _HashedTuple(args)
+
+
+def typedkey(*args, **kwargs):
+    """Return a typed cache key for the specified hashable arguments."""
+
+    key = hashkey(*args, **kwargs)
+    key += tuple(type(v) for v in args)
+    key += tuple(type(v) for _, v in sorted(kwargs.items()))
+    return key