gcsio: reduce number of get requests in function calls

[shunping]

We replace client.get_bucket() with client.bucket(), and bucket.get_blob() with bucket.blob() in a few places where a lightweight instance of bucket/blob is sufficient for the function calls.

The fix reduces unnecessary get requests (from get_bucket and get_blob) in the following gcsio apis:

• open
• delete
• delete_batch
• copy
• copy_batch
• list_files

addresses #28398

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[lgeiger]

Should .get_bucket in self._gcs_object also be replaced with .bucket?

It seems like bucket.get_blob already makes a HTTP request to check whether the blob exists, or am I missing something?

[lgeiger]

Looking at the codebase again, maybe it also makes sense to adapt the code paths here and here to be consistent.

[shunping]

Should .get_bucket in self._gcs_object also be replaced with .bucket?

It seems like bucket.get_blob already makes a HTTP request to check whether the blob exists, or am I missing something?

I checked the code, it should be fine to replace the get_bucket() with bucket() within _gcs_object().

[shunping]

Run Python_Coverage PreCommit

[Abacn]

Good point. That was why it needed to be range(2) or range(4) in delete_batch and copy_batch

[johnjcasey]

LGTM

[Abacn]

Checked that tests passed and Comments are resolved, merging for now

[Abacn]

seems this change need to make test change accordingly. PythonPostCommit failing apache_beam.io.gcp.gcsfilesystem_integration_test.GcsFileSystemIntegrationTest.test_rename_error failing as it was on the premise of the request of delete one file returning two response code CC: @shunping

https://github.com/apache/beam/runs/21333859365