Fix RuntimeError caused by change dict size during iteration

vetal4444 · vetal4444 · commit aeb71aad7769 · 2017-02-15T14:54:23.000+02:00
diff --git a/cassandra/cluster.py b/cassandra/cluster.py
@@ -2242,7 +2242,7 @@ def prepare_on_all_hosts(self, query, excluded_host):
         Intended for internal use only.
         """
         futures = []
-        for host in self._pools.keys():
+        for host in tuple(self._pools.keys()):
             if host != excluded_host and host.is_up:
                 future = ResponseFuture(self, PrepareMessage(query=query), None, self.default_timeout)
 
