fix: fix mypy errors

[parthea]

WIP

[gemini-code-assist]

Summary of Changes

Hello @parthea, 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 focuses on improving the type checking robustness of the google-cloud-automl library by addressing existing mypy errors. It refines how optional dependencies are handled and ensures that mypy has the necessary type information for external libraries, leading to a cleaner and more reliable codebase.

Highlights

• Refactored Optional Dependency Checks: The pull request refactors how optional dependencies (pandas and google.cloud.storage) are checked for availability in gcs_client.py. Instead of checking if the imported module is None, dedicated boolean flags (_PANDAS_INSTALLED and _STORAGE_INSTALLED) are now used to indicate successful import.
• Mypy Type Ignore for Google Cloud Storage: A type: ignore comment has been added to the google.cloud.storage import statement in gcs_client.py to suppress mypy errors related to a known upstream issue, ensuring smoother type checking.
• Added Pandas Type Stubs: The noxfile.py has been updated to include pandas-stubs in the mypy session dependencies. This provides necessary type information for the pandas library, improving the accuracy and completeness of static type analysis.

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[gemini-code-assist]

Code Review

This pull request aims to fix mypy errors, and the changes in noxfile.py to add pandas-stubs are correct. However, the changes in google/cloud/automl_v1beta1/services/tables/gcs_client.py to handle optional dependencies using boolean flags introduce a new problem for static analysis: mypy will report a NameError because the module names (pandas, storage) are not defined if their respective imports fail.

I've provided suggestions to revert to the more standard pattern of setting the module variable to None on ImportError. This resolves the NameError for mypy. The type: ignore for the storage import is preserved as it seems necessary to resolve a separate mypy issue with that library. With these changes, the mypy errors should be correctly resolved.

[gemini-code-assist]

This approach of using boolean flags to track optional dependencies can introduce a NameError for static type checkers like mypy. If an import fails, the module name is not defined, which will cause a mypy error on later usage (e.g., pandas.DataFrame).

The original pattern of setting the module to None on ImportError is more robust. The mypy errors can be fixed by other means. For storage, the type: ignore you've added is correct. For pandas, mypy should correctly handle the if pandas is None: raise type guard, especially with pandas-stubs installed.

I suggest reverting this block to the conventional pattern, which will also require reverting the checks below.

Suggested change

	try:
	import pandas
	_PANDAS_INSTALLED = True
	except ImportError: # pragma: NO COVER
	pandas = None
	_PANDAS_INSTALLED = False
	try:
	from google.cloud import storage
	# TODO(https://github.com/googleapis/python-storage/issues/318):
	# Remove `type: ignore` once this bug is fixed
	from google.cloud import storage # type: ignore
	_STORAGE_INSTALLED = True
	except ImportError: # pragma: NO COVER
	storage = None
	_STORAGE_INSTALLED = False
	try:
	import pandas
	except ImportError: # pragma: NO COVER
	pandas = None
	try:
	# TODO(https://github.com/googleapis/python-storage/issues/318):
	# Remove `type: ignore` once this bug is fixed
	from google.cloud import storage # type: ignore
	except ImportError: # pragma: NO COVER
	storage = None

[gemini-code-assist]

To align with the suggested change to the import pattern, this check should be reverted to if storage is None:.

Suggested change

	if not _STORAGE_INSTALLED:
	if storage is None:

[gemini-code-assist]

To align with the suggested change to the import pattern, this check should be reverted to if pandas is None:.

Suggested change

	if not _PANDAS_INSTALLED:
	if pandas is None: