[BEAM-10418] Support type hint annotations on CombineFn add_input() and extract_output()

• Type: Improvement
• Status: Triage Needed
• Priority: P3
• Resolution: Unresolved
• Component/s: sdk-py-core
• Labels: types
• Assignee: Unassigned
• Reporter: Matt McDonald
• Created: 07/Jul/20 20:14
• Updated: 2 days ago 18:15

Description

Similar to the tweaks for supporting native type hints on the PTransform.expand() method (https://issues.apache.org/jira/browse/BEAM-10258), it would be beneficial if the CombineFn class also received similar treatment, offering a way to provide type hints through the native Python hinting interface.

Adding hints to the CombineFn's add_input() and extract_output() methods should be sufficient for providing the equivalent behavior of annotating the class with beam typehint decorators, e.g.,

@beam.typehints.with_input_types(int)
@beam.typehints.with_output_types(bool)
class MyCombineFn(CombineFn):
  ...

vs

class MyCombineFn(CombineFn):
  def add_input(self, accumulator: float, element: int):
    ...

  def extract_output(self, accumulator: float) -> bool
    ...