Add exception chaining

[shaheeramjad]

Description

This PR adds exception chaining (raise ... from) throughout the Python SDK to preserve error context and improve debuggability. When exceptions are re-raised without chaining, the original traceback context is lost, making it difficult to identify root causes of failures.

Changes Made

1. CloudSQLEnrichmentHandler (transforms/enrichment_handlers/cloudsql.py)

   • Added from e to exception re-raises in _execute_query() method
   • Preserves original database exception context when database operations fail

2. Process Utilities (utils/processes.py)

   • Added exception chaining for OSError and CalledProcessError in call(), check_call(), and check_output() functions
   • Preserves original subprocess exception context when external executables fail

3. Core Transforms (transforms/core.py)

   • Improved exception logging to include exc_info=True when failure callbacks fail
   • Preserves full traceback in logs for better debugging

Benefits

• Better Debugging: Developers can now see the full error chain when exceptions occur
• Faster Issue Resolution: Root causes are immediately visible in stack traces
• Python Best Practice: Follows PEP 3134 (Exception Chaining and Embedded Tracebacks)
• Improved Error Messages: More informative stack traces for production debugging

Example

Before:

except Exception as e:
    raise RuntimeError(f"Database operation failed: {e}")

After:

except Exception as e:
    raise RuntimeError(f"Database operation failed: {e}") from e

Now when this fails, developers see:

RuntimeError: Database operation failed: connection timeout
The above exception was the direct cause of the following exception:
ConnectionTimeoutError: Failed to connect within 30 seconds
  [full original traceback here]

Testing

• Syntax validation passed
• No linter errors introduced
• Changes preserve existing behavior (only adds exception context)
• Backward compatible (no breaking changes)

---

Checklist

• Mention the appropriate issue in your description (addresses Enhancement: Add exception chaining (raise ... from) throughout codebase to preserve error context #37422)
• Update CHANGES.md with noteworthy changes
• If this contribution is large, please file an Apache Individual Contributor License Agreement. (Not required - this is a small code quality improvement)

---

Related

• Addresses issue referenced in .pylintrc line 139: #TODO(https://github.com/apache/beam/issues/21169)
• Follows Python PEP 3134 standard for exception chaining
• Related to GitHub Issue Enhancement: Add exception chaining (raise ... from) throughout codebase to preserve error context #37422

---

[gemini-code-assist]

Summary of Changes

Hello @shaheeramjad, 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 significantly improves the debuggability of the Python SDK by implementing explicit exception chaining (raise ... from) across several critical components. By linking re-raised exceptions to their original causes, the changes ensure that developers have access to complete error tracebacks, which is essential for quickly identifying and resolving the root causes of failures. This enhancement aligns with Python's best practices for error handling and contributes to more robust and informative error reporting.

Highlights

• CloudSQL Enrichment Handler: Implemented exception chaining in the _execute_query method within CloudSQLEnrichmentHandler to preserve the original database exception context when operations fail.
• Process Utilities: Added exception chaining for OSError and subprocess.CalledProcessError in the call(), check_call(), and check_output() functions, ensuring the original subprocess exception context is retained.
• Core Transforms Logging: Enhanced exception logging in exception_handling_wrapper_do_fn_custom_process by including exc_info=True when on_failure_callback itself fails, providing a full traceback in the logs.

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[github-actions]

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[shaheeramjad]

assign set of reviewers

[github-actions]

Assigning reviewers:

R: @claudevdm for label python.

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[shaheeramjad]

assign to next reviewer

[shaheeramjad]

HI @damccorm,
Just a gentle ping for review when you have time. Thanks!

[damccorm]

If we're chaining the exception, do we still need to include the exception in the RuntimeError message?

[damccorm]

Same question exists below in this file as well

[shaheeramjad]

With from e, the cause is in cause and the traceback, so we don’t need to include the exception in the message.
I kept it in because in many environments only the top-level exception message is logged or shown (e.g. in alerts or dashboards). In those cases, "Database operation failed" alone doesn’t tell you the real error, while f"Database operation failed: {e}" stays useful. It’s also a common Python pattern to add context and still include the original error in the wrapper message.
If you prefer to rely on the chain and keep messages minimal, I’m happy to change to e.g. raise RuntimeError("Database operation failed") from e and remove {e} from the message. Happy to follow whatever convention you prefer for this project.