learning/tour-of-beam/learning-content/triggers/processing-trigger/python-example/task.py

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# beam-playground:
#   name: processing-trigger
#   description: Processing trigger example.
#   multifile: false
#   context_line: 52
#   categories:
#     - Quickstart
#   complexity: ADVANCED
#   tags:
#     - hellobeam

import apache_beam as beam
from apache_beam import window
from apache_beam.transforms.trigger import AfterWatermark, AfterProcessingTime, AccumulationMode, AfterCount
from apache_beam.transforms.window import FixedWindows
from apache_beam.transforms import trigger


# Output PCollection
class Output(beam.PTransform):
    class _OutputFn(beam.DoFn):
        def __init__(self, prefix=''):
            super().__init__()
            self.prefix = prefix

        def process(self, element):
            print(self.prefix+str(element))

    def __init__(self, label=None,prefix=''):
        super().__init__(label)
        self.prefix = prefix

    def expand(self, input):
        input | beam.ParDo(self._OutputFn(self.prefix))

with beam.Pipeline() as p:
  (p | beam.Create(['Hello Beam','It`s trigger'])
     | 'window' >>  beam.WindowInto(FixedWindows(2),
                                                trigger=trigger.AfterProcessingTime(1),
                                                accumulation_mode=trigger.AccumulationMode.DISCARDING) \
     | 'Log words' >> Output())