Remove type coercion of FinalizeWrite in iobase.py

[liaopeiyuan]

_finalize_write's output type is TimestampedValue, not str, so when runtime_type_check is set to True in TypeOptions, it would raise a SimpleTypeHintError with the following details: apache_beam.typehints.decorators.TypeCheckError: According to type-hint expected output should be of type <class 'str'>. Instead, received '<apache_beam.transforms.window.TimestampedValue object at 0x7a303057cd10>', an instance of type <class 'apache_beam.transforms.window.TimestampedValue'>

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[liaopeiyuan]

assign set of reviewers (unclear why Prism Python checks are failing)

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[Abacn]

Thanks for the fix. There might be something need clarification here. TimestampedValue is a special value type in Beam. If an element wrapped as a TimestampedValue, in downstream the timestamp becomes a metadata for this element, while the element is still the original one, e.g.

_ = p | beam.Create(["1", "2", "3"]) | beam.Map(lambda x: window.TimestampedValue(x, timestamp.MAX_TIMESTAMP)) | beam.Map(print)
presult = p.run()

it prints the str itself instead of TimestampedValue(1)

Seems this convention conflicts with type check also part of Beam SDK. cc: @jrmccluskey @tvalentyn may have a solution here

[tvalentyn]

Thanks @liaopeiyuan

I would create a bug with a reproducible example. Agree with @Abacn that changing the type coercion might not be the best solution here. I am seeing that some logic in type checking machinery that suggests, TimetampedValue instances should be compared by the type they are enveloping:

beam/sdks/python/apache_beam/typehints/typecheck.py

Line 158 in dc7426f

if isinstance(o, TimestampedValue) and hasattr(o, "__orig_class__"):

I would check why that is not happening.