Avoid RequestResponseIO throttler access when throttler is absent

[hoang-shyftplan]

Description

• Guard the post-call success throttler metric callback in _CallDoFn with the same _throttler presence check used for pre-call throttling.
• Prevent crashes when RequestResponseIO is used with no throttler / non-default throttling path.
• This addresses the reported AttributeError: 'NoneType' object has no attribute 'throttler' on successful calls.

Testing

Not run (no test execution requested).

[gemini-code-assist]

Summary of Changes

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This pull request addresses a runtime crash in RequestResponseIO that occurs when a throttler is not configured. By ensuring the throttler is present before attempting to record successful request metrics, the implementation becomes more robust against non-default throttling configurations.

Highlights

• Throttler safety check: Added a conditional check for the existence of the throttler object before accessing it in the successful request callback to prevent potential AttributeError exceptions.

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[gemini-code-assist]

Code Review

This pull request adds a safety check in sdks/python/apache_beam/io/requestresponse.py to ensure self._throttler is defined before calling successful_request. The reviewer recommended using an explicit is not None check instead of implicit truthiness to comply with PEP 8 style guidelines.

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[gemini-code-assist]

According to PEP 8, comparisons to singletons like None should always be done with is or is not, never the equality operators or implicit truthiness checks, especially when testing whether an optional variable or argument that defaults to None was set. Using is not None is safer and more explicit.

Suggested change

	if self._throttler:
	self._throttler.throttler.successful_request(req_time * MSEC_TO_SEC)
	if self._throttler is not None:
	self._throttler.throttler.successful_request(req_time * MSEC_TO_SEC)

References

1. PEP 8: Comparisons to singletons like None should always be done with 'is' or 'is not', never the equality operators. Also, beware of writing 'if x' when you really mean 'if x is not None'. ^(link)