sdks/python/apache_beam/runners/dataflow/ptransform_overrides.py

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"""Ptransform overrides for DataflowRunner."""

# pytype: skip-file

from apache_beam.pipeline import PTransformOverride


class NativeReadPTransformOverride(PTransformOverride):
  """A ``PTransformOverride`` for ``Read`` using native sources.

  The DataflowRunner expects that the Read PTransform using native sources act
  as a primitive. So this override replaces the Read with a primitive.
  """
  def matches(self, applied_ptransform):
    # Imported here to avoid circular dependencies.
    # pylint: disable=wrong-import-order, wrong-import-position
    from apache_beam.io import Read

    # Consider the native Read to be a primitive for Dataflow by replacing.
    return (
        isinstance(applied_ptransform.transform, Read) and
        not getattr(applied_ptransform.transform, 'override', False) and
        hasattr(applied_ptransform.transform.source, 'format'))

  def get_replacement_transform(self, ptransform):
    # Imported here to avoid circular dependencies.
    # pylint: disable=wrong-import-order, wrong-import-position
    from apache_beam import pvalue
    from apache_beam.io import iobase

    # This is purposely subclassed from the Read transform to take advantage of
    # the existing windowing, typing, and display data.
    class Read(iobase.Read):
      override = True

      def expand(self, pbegin):
        return pvalue.PCollection.from_(pbegin)

    # Use the source's coder type hint as this replacement's output. Otherwise,
    # the typing information is not properly forwarded to the DataflowRunner and
    # will choose the incorrect coder for this transform.
    return Read(ptransform.source).with_output_types(
        ptransform.source.coder.to_type_hint())