Cheatsheet: DoFn

import apache_beam as beam

class ParseRecordFn(beam.DoFn):
    def setup(self):
        # Called once per worker start (good for client initialization)
        self.client = initialize_database_client()

    def start_bundle(self):
        # Called once per element bundle processing start
        self.batch = []

    def process(self, element):
        # Main entrypoint: yields zero, one, or multiple outputs
        if element.is_valid:
            yield element

    def finish_bundle(self):
        # Called at the end of element bundle execution
        pass

    def teardown(self):
        # Called once when worker halts (closes connections)
        self.client.close()