Fix MatchContinuously translation

[ahmedabu98]

I was trying to use Python's apache_beam.io.fileio.MatchContinuously in a YAML pipeline that had a downstream Java sink, and kept running into this error:

TypeError: no default __reduce__ due to non-trivial __cinit__
...

RuntimeError: Unable to translate MatchContinuously/GetFilePattern

This fix allows MatchContinuously to get translated normally. Just needed to use a local variable to avoid having to serialize self

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a serialization issue in the Apache Beam Python SDK's MatchContinuously transform. By decoupling the file pattern from the class instance during the mapping process, the transform can now be correctly translated for cross-language pipelines, resolving runtime errors encountered when integrating with Java-based sinks.

Highlights

• Serialization Fix: Modified the MatchContinuously transform to use a local variable for the file pattern, preventing the need to serialize the entire self object during pipeline translation.
• Bug Resolution: Resolved a TypeError and RuntimeError occurring when using MatchContinuously in YAML pipelines with downstream Java sinks.

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[ahmedabu98]

R: @chamikaramj

[gemini-code-assist]

Code Review

This pull request refactors the MatchContinuously transform in sdks/python/apache_beam/io/fileio.py by extracting self.file_pattern into a local variable before using it inside the lambda function. This is a standard practice in Apache Beam to avoid serializing the entire class instance (self) when executing the pipeline. There are no review comments to evaluate, and I have no additional feedback to provide.

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[chamikaramj]

LGTM. Thanks!