MAINT: Use more direct check for WeakSet.

Author: Scott Sanderson

cloudpickle/cloudpickle.py

@@ -859,7 +859,7 @@ def save_not_implemented(self, obj):
     dispatch[type(NotImplemented)] = save_not_implemented
 
     # WeakSet was added in 2.7.
-    if sys.version_info >= (2, 7):
+    if hasattr(weakref, 'WeakSet'):
         def save_weakset(self, obj):
             self.save_reduce(weakref.WeakSet, (list(obj),))
 

tests/cloudpickle_test.py

@@ -46,7 +46,7 @@
 from .testutils import subprocess_pickle_echo
 
 
-HAVE_WEAKSET = sys.version_info >= (2, 7)
+HAVE_WEAKSET = hasattr(weakref, 'WeakSet')
 
 
 def pickle_depickle(obj):