Use proper clock if possible

powerline/lib/memoize.py

@@ -1,7 +1,12 @@
 # vim:fileencoding=utf-8:noet
 
 from functools import wraps
-import time
+try:
+	# Python>=3.3, the only valid clock source for this job
+	from time import monotonic as time
+except ImportError:
+	# System time, is affected by clock updates.
+	from time import time
 
 
 def default_cache_key(**kwargs):
@@ -28,10 +33,13 @@ class memoize(object):
 				cached = self.cache.get(key, None)
 			except TypeError:
 				return func(**kwargs)
-			if cached is None or time.time() - cached['time'] > self.timeout:
+			# Handle case when time() appears to be less then cached['time'] due 
+			# to clock updates. Not applicable for monotonic clock, but this 
+			# case is currently rare.
+			if cached is None or not (cached['time'] < time() < cached['time'] + self.timeout):
 				cached = self.cache[key] = {
 					'result': func(**kwargs),
-					'time': time.time(),
+					'time': time(),
 					}
 			return cached['result']
 		return decorated_function