Never trigger for Python.

robertwb · robertwb · commit 6eefa9c30d18 · 2020-06-03T10:24:00.000-07:00
diff --git a/sdks/python/apache_beam/transforms/trigger.py b/sdks/python/apache_beam/transforms/trigger.py
@@ -256,7 +256,7 @@ def from_runner_api(proto, context):
         'always': Always,
         'default': DefaultTrigger,
         'element_count': AfterCount,
-        # never
+        'never': Never,
         'or_finally': OrFinally,
         'repeat': Repeatedly,
     }[proto.WhichOneof('trigger')].from_runner_api(proto, context)
@@ -408,6 +408,48 @@ def to_runner_api(self, context):
         always=beam_runner_api_pb2.Trigger.Always())
 
 
+class Never(TriggerFn):
+  """A trigger that never fires.
+  """
+  def __init__(self):
+    pass
+
+  def __repr__(self):
+    return 'Never'
+
+  def __eq__(self, other):
+    return type(self) == type(other)
+
+  def __hash__(self):
+    return hash(type(self))
+
+  def on_element(self, element, window, context):
+    pass
+
+  def on_merge(self, to_be_merged, merge_result, context):
+    pass
+
+  def has_ontime_pane(self):
+    False
+
+  def reset(self, window, context):
+    pass
+
+  def should_fire(self, time_domain, watermark, window, context):
+    return False
+
+  def on_fire(self, watermark, window, context):
+    return True
+
+  @staticmethod
+  def from_runner_api(proto, context):
+    return Never()
+
+  def to_runner_api(self, context):
+    return beam_runner_api_pb2.Trigger(
+        never=beam_runner_api_pb2.Trigger.Never())
+
+
 class AfterWatermark(TriggerFn):
   """Fire exactly once when the watermark passes the end of the window.
 
diff --git a/sdks/python/apache_beam/transforms/trigger_test.py b/sdks/python/apache_beam/transforms/trigger_test.py
@@ -59,6 +59,7 @@
 from apache_beam.transforms.trigger import DefaultTrigger
 from apache_beam.transforms.trigger import GeneralTriggerDriver
 from apache_beam.transforms.trigger import InMemoryUnmergedState
+from apache_beam.transforms.trigger import Never
 from apache_beam.transforms.trigger import Repeatedly
 from apache_beam.transforms.trigger import TriggerFn
 from apache_beam.transforms.window import FixedWindows
@@ -518,6 +519,28 @@ def format_result(k_v):
                   'B-3': {10, 15, 16},
               }.items())))
 
+  def test_never(self):
+    with TestPipeline() as p:
+
+      def construct_timestamped(k_t):
+        return TimestampedValue((k_t[0], k_t[1]), k_t[1])
+
+      def format_result(k_v):
+        return ('%s-%s' % (k_v[0], len(k_v[1])), set(k_v[1]))
+
+      result = (
+          p
+          | beam.Create([1, 1, 2, 3, 4, 5, 10, 11])
+          | beam.FlatMap(lambda t: [('A', t), ('B', t + 5)])
+          | beam.Map(construct_timestamped)
+          | beam.WindowInto(
+              FixedWindows(10),
+              trigger=Never(),
+              accumulation_mode=AccumulationMode.DISCARDING)
+          | beam.GroupByKey()
+          | beam.Map(format_result))
+      assert_that(result, equal_to([]))
+
   def test_multiple_accumulating_firings(self):
     # PCollection will contain elements from 1 to 10.
     elements = [i for i in range(1, 11)]
