Merge pull request #809 from deniszh/backport/1.1.x/pr-806_pr-806_pr-…

…806_pr-808

[1.1.x] import setUpRandomResolver only for new Twisted | Keeping it simple | spacing | Taming E501 in linter

lib/carbon/client.py

@@ -12,7 +12,6 @@
 from carbon.util import pickle
 from carbon.util import PluginRegistrar
 from carbon.util import enableTcpKeepAlive
-from carbon.resolver import setUpRandomResolver
 from carbon import instrumentation, log, pipeline, state
 
 try:
@@ -29,6 +28,11 @@
 except ImportError:
     log.debug("Couldn't import signal module")
 
+try:
+    from carbon.resolver import setUpRandomResolver
+except ImportError:
+    setUpRandomResolver = None
+
 
 SEND_QUEUE_LOW_WATERMARK = settings.MAX_QUEUE_SIZE * settings.QUEUE_LOW_WATERMARK_PCT
 
@@ -528,7 +532,11 @@ def __init__(self, router):
         # If we decide to open multiple TCP connection to a replica, we probably
         # want to try to also load-balance accross hosts. In this case we need
         # to make sure rfc3484 doesn't get in the way.
-        setUpRandomResolver(reactor)
+        if setUpRandomResolver:
+          setUpRandomResolver(reactor)
+        else:
+          print("Import error, Twisted >= 17.1.0 needed for using DESTINATION_POOL_REPLICAS.")
+          raise SystemExit(1)
 
     self.router = router
     self.client_factories = {}  # { destination : CarbonClientFactory() }