Testing the boolean nature of Pipeline instance should always return True.

Prior to this, pipeline instances used __len__() which returns the number
of queued commands on the pipeline. When there were no queued commands,
the pipeline instance would evaluate to 0 or False.

Fixes #994

Author: andymccurdy

CHANGES

@@ -6,6 +6,10 @@
     * Removed support for end of life Python 3.4.
     * Added support for all ACL commands in Redis 6. Thanks @IAmATeaPot418
       for helping.
+    * Pipeline instances now always evaluate to True. Prior to this change,
+      pipeline instances relied on __len__ for boolean evaluation which
+      meant that pipelines with no commands on the stack would be considered
+      False. #994
 * 3.3.11
     * Further fix for the SSLError -> TimeoutError mapping to work
       on obscure releases of Python 2.7.

redis/client.py

@@ -3703,6 +3703,14 @@ def __del__(self):
     def __len__(self):
         return len(self.command_stack)
 
+    def __nonzero__(self):
+        "Pipeline instances should  always evaluate to True on Python 2.7"
+        return True
+
+    def __bool__(self):
+        "Pipeline instances should  always evaluate to True on Python 3+"
+        return True
+
     def reset(self):
         self.command_stack = []
         self.scripts = set()

tests/test_pipeline.py

@@ -6,6 +6,11 @@
 
 
 class TestPipeline(object):
+    def test_pipeline_is_true(self, r):
+        "Ensure pipeline instances are not false-y"
+        with r.pipeline() as pipe:
+            assert pipe
+
     def test_pipeline(self, r):
         with r.pipeline() as pipe:
             (pipe.set('a', 'a1')
@@ -28,17 +33,14 @@ def test_pipeline_length(self, r):
         with r.pipeline() as pipe:
             # Initially empty.
             assert len(pipe) == 0
-            assert not pipe
 
             # Fill 'er up!
             pipe.set('a', 'a1').set('b', 'b1').set('c', 'c1')
             assert len(pipe) == 3
-            assert pipe
 
             # Execute calls reset(), so empty once again.
             pipe.execute()
             assert len(pipe) == 0
-            assert not pipe
 
     def test_pipeline_no_transaction(self, r):
         with r.pipeline(transaction=False) as pipe: