Allow Pipeline.execute() to execute on empty command stack if it is watching keys

3 files changed, 20 insertions, 2 deletions

diff --git a/CHANGES b/CHANGES
index 73d2d4e..7c0d888 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,9 +1,14 @@
+* (IN DEVELOPMENT)
+    * Allow empty pipelines to be executed if there are WATCHed keys.
+      This is a convenient way to test if any of the watched keys changed
+      without actually running any other commands. Thanks @brianmaissy.
+      #1233, #1234
 * 3.3.11
     * Further fix for the SSLError -> TimeoutError mapping to work
       on obscure releases of Python 2.7.
 * 3.3.10
     * Fixed a potential error handling bug for the SSLError -> TimeoutError
-      mapping introduced in 3.3.9. hanks @zbristow. #1224
+      mapping introduced in 3.3.9. Thanks @zbristow. #1224
 * 3.3.9
     * Mapped Python 2.7 SSLError to TimeoutError where appropriate. Timeouts
       should now consistently raise TimeoutErrors on Python 2.7 for both
diff --git a/redis/client.py b/redis/client.py
index df1ebfd..1e5ca02 100755
--- a/redis/client.py
+++ b/redis/client.py
@@ -3670,7 +3670,7 @@ class Pipeline(Redis):
     def execute(self, raise_on_error=True):
         "Execute all the commands in the current pipeline"
         stack = self.command_stack
-        if not stack:
+        if not stack and not self.watching:
             return []
         if self.scripts:
             self.load_scripts()
diff --git a/tests/test_pipeline.py b/tests/test_pipeline.py
index 2e2507a..264a64f 100644
--- a/tests/test_pipeline.py
+++ b/tests/test_pipeline.py
@@ -191,6 +191,19 @@ class TestPipeline(object):
 
             assert not pipe.watching
 
+    def test_watch_failure_in_empty_transaction(self, r):
+        r['a'] = 1
+        r['b'] = 2
+
+        with r.pipeline() as pipe:
+            pipe.watch('a', 'b')
+            r['b'] = 3
+            pipe.multi()
+            with pytest.raises(redis.WatchError):
+                pipe.execute()
+
+            assert not pipe.watching
+
     def test_unwatch(self, r):
         r['a'] = 1
         r['b'] = 2