Add caching decorators

(imported from commit 7a4d9257ea8c6a86a5ffb498f726c4c2eb42bc9f)

zephyr/lib/cache.py

@@ -0,0 +1,44 @@
+import django.core.cache
+
+def cache_with_key(keyfunc):
+    """Decorator which applies Django caching to a function.
+
+       Decorator argument is a function which computes a cache key
+       from the original function's arguments.  You are responsible
+       for avoiding collisions with other uses of this decorator or
+       other uses of caching."""
+
+    def decorator(func):
+        djcache = django.core.cache.cache
+
+        def func_with_caching(*args, **kwargs):
+            key = keyfunc(*args, **kwargs)
+            val = djcache.get(key)
+
+            # Values are singleton tuples so that we can distinguish
+            # a result of None from a missing key.
+            if val is not None:
+                return val[0]
+
+            val = func(*args, **kwargs)
+            djcache.set(key, (val,))
+            return val
+
+        return func_with_caching
+
+    return decorator
+
+def cache(func):
+    """Decorator which applies Django caching to a function.
+
+       Uses a key based on the function's name, filename, and
+       the repr() of its arguments."""
+
+    func_uniqifier = '%s-%s' % (func.func_code.co_filename, func.func_name)
+
+    def keyfunc(*args, **kwargs):
+        # Django complains about spaces because memcached rejects them
+        key = func_uniqifier + repr((args, kwargs))
+        return key.replace('-','--').replace(' ','-s')
+
+    return cache_with_key(keyfunc)(func)