Fix truncating file handle

[shunping]

A few tests in the Python Precommit suite, including YamlTestingTest::test_create and IOTest::test_read_fwf, InlinePythonTest::test_line_69, have been reporting ValueError and AttributeError exceptions during execution (https://github.com/apache/beam/actions/runs/25576871651/job/75086176283).

The traceback is shown below:

  Traceback (most recent call last):
    File "/Users/runner/work/beam/beam/sdks/python/apache_beam/dataframe/io.py", line 587, in flush
      self._underlying.flush()
      ~~~~~~~~~~~~~~~~~~~~~~^^
  ValueError: I/O operation on closed file.
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "/Users/runner/work/beam/beam/sdks/python/target/.tox/py313-macos/lib/python3.13/site-packages/apache_beam/runners/worker/bundle_processor.py", line 235, in process_encoded
      self.output(decoded_value)
      ~~~~~~~~~~~^^^^^^^^^^^^^^^
  AttributeError: '_TruncatingFileHandle' object has no attribute 'close'. Did you mean: 'closed'?

The issue occurs when flush() is called on a _TruncatingFileHandle after the underlying file has already been closed, leading to a ValueError. This exception then triggers a secondary AttributeError because _TruncatingFileHandle lacked a close() method

In this PR, we fixed the handling of close and flush operations within _TruncatingFileHandle.

[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 stability issues in the Apache Beam Python SDK's _TruncatingFileHandle class. By ensuring that file operations are only performed if the underlying stream is open and adding necessary error handling, the changes prevent intermittent crashes during I/O operations that were previously causing failures in the Precommit test suite.

Highlights

• Improved File Handle State Management: Updated the closed property in _TruncatingFileHandle to correctly reflect the state of the underlying file object.
• Robust Flush and Close Operations: Added defensive checks to flush() and implemented a close() method in _TruncatingFileHandle to prevent ValueError and AttributeError exceptions when interacting with already closed files.
• Regression Testing: Added a new test case test_truncating_filehandle_flush_on_closed_stream to verify that flushing a closed stream no longer triggers exceptions.

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[gemini-code-assist]

Code Review

This pull request updates the _TruncatingFileHandle class to dynamically report its closed status based on the underlying stream and adds safer implementations for flush and close to handle closed streams gracefully. A new test case was also added to verify flush behavior. The review feedback suggests narrowing the exception handling in the close method to avoid suppressing unrelated errors and extending the unit test to explicitly cover the newly added close functionality.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.75%. Comparing base (81828fd) to head (7e4ee0a).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
sdks/python/apache_beam/dataframe/io.py	50.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #38425      +/-   ##
============================================
+ Coverage     55.74%   55.75%   +0.01%     
  Complexity     2095     2095              
============================================
  Files          1099     1099              
  Lines        172219   172287      +68     
  Branches       1350     1350              
============================================
+ Hits          95995    96065      +70     
+ Misses        73829    73827       -2     
  Partials       2395     2395              

Flag	Coverage Δ
python	79.83% <50.00%> (+0.01%)	⬆️

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[github-actions]

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