Allow parquet import to be None

[damccorm]

Installing pyarrow can be painful, especially on macs with M1s (I've run into this), and it isn't necessary for most python development. At the same time, doing anything involving conftest.py causes parquetio.py to be loaded[1], and this currently fails when pyarrow is not installed.

This is because even though pyarrow imports are guarded behind a try/except block, we assume that pa is defined later in the file when we enforce the pa.Table type. This works around that issue by creating a variable that holds pa.Table when it is defined, and None otherwise. Invoking these functions will still fail, but now you can load the file without issues.

[1] The dependency path that errors is:

ImportError while loading conftest '/Users/dannymccormick/beam/sdks/python/conftest.py'.
conftest.py:26: in <module>
    from apache_beam.options import pipeline_options
apache_beam/__init__.py:88: in <module>
    from apache_beam import io
apache_beam/io/__init__.py:28: in <module>
    from apache_beam.io.parquetio import *
apache_beam/io/parquetio.py:174: in <module>
    class _ArrowTableToBeamRows(DoFn):
apache_beam/io/parquetio.py:179: in _ArrowTableToBeamRows
    def process(self, element) -> Iterator[pa.Table]:
E   AttributeError: 'NoneType' object has no attribute 'Table'

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[gemini-code-assist]

Summary of Changes

Hello @damccorm, 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 common issue where the apache_beam.io.parquetio module would fail to load if the pyarrow library was not installed, even when Parquet-related functionalities were not being used. By introducing a conditional assignment for pyarrow.Table and using this new variable for type hints, the module can now be imported without errors, significantly improving the developer experience for users who do not require pyarrow.

Highlights

• Optional PyArrow Dependency: Modified the parquetio.py module to gracefully handle cases where pyarrow is not installed, preventing import errors.
• Conditional Type Hinting: Introduced a new variable, paTable, to conditionally store pyarrow.Table or None, which is then used for type hints throughout the module.
• Improved Module Loading: Ensures that apache_beam.io.parquetio can be loaded successfully even without pyarrow installed, resolving AttributeError issues during module import for users who do not require Parquet functionalities.

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[github-actions]

Checks are failing. Will not request review until checks are succeeding. If you'd like to override that behavior, comment assign set of reviewers

[Abacn]

Looks like it is intended to be optional but due to typehint this was not effective

[github-actions]

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