feat: autocommit sample

[AlisskaPie]

These changes have been moved from python-spanner-django PR.

[snippet-bot]

Here is the summary of changes.

You added 1 region tag.

• samples/samples/autocommit.py:14, tag spanner_enable_autocommit_mode

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[IlyaFaer]

I see an error ModuleNotFoundError: No module named sqlparse here. We already have two PRs with adding this dependency:
https://github.com/googleapis/python-spanner/pull/171/files
https://github.com/googleapis/python-spanner/pull/168/files

[c24t]

Looks like I gave you some bad info in googleapis/python-spanner-django#552 (comment), making samples a package causes import errors for other sample modules:

________________ ERROR collecting samples/samples/backup_sample_test.py _______________
ImportError while importing test module 'src/python-spanner/samples/samples/backup_sample_test.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.pyenv/versions/3.8.2/lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
backup_sample_test.py:21: in <module>
    import backup_sample
E   ModuleNotFoundError: No module named 'backup_sample'
__________________ ERROR collecting samples/samples/quickstart_test.py _______________
ImportError while importing test module 'src/python-spanner/samples/samples/quickstart_test.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.pyenv/versions/3.8.2/lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
quickstart_test.py:21: in <module>
    import quickstart
E   ModuleNotFoundError: No module named 'quickstart'
___________________ ERROR collecting samples/samples/snippets_test.py _______________
ImportError while importing test module 'src/python-spanner/samples/samples/snippets_test.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.pyenv/versions/3.8.2/lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
snippets_test.py:21: in <module>
    import snippets
E   ModuleNotFoundError: No module named 'snippets'

Should be fixed now.

[AlisskaPie]

Looks like I gave you some bad info in googleapis/python-spanner-django#552 (comment), making samples a package causes import errors for other sample modules:
...
Should be fixed now.

Thanks for commiting code! Errors in importing other sample modules have disappeared.

[larkee]

Mostly LGTM, just the one concern

[larkee]

Why does the user need to initialise a private variable? Can this not be initialised as part of the cursor factory?

[AlisskaPie]

Thank you for the review! And sorry for the delayed answer.
I've made an update and placed this part in the test.

[larkee]

This is not quite what I meant. The sample now looks as I would expect but I'm unclear as to why you still need to set cursor._checksum in the test. Is there a reason that _checksum defaults to None? Could it be updated to ResultsChecksum() instead?

[c24t]

Re: #172 (comment), it looks like the tests pass without setting cursor._checksum and I see you didn't need this line in googleapis/python-spanner-django#552. Any reason not to remove it here?

The other suggested changes are just formatting and liberating some imports.

As in googleapis/python-spanner-django#552 (review), I think the sample would be more useful if it showed the different behavior with autocommit on/off, but this sample looks fine to me otherwise. LGTM with my suggested changes.

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[IlyaFaer]

@googlebot I consent.

[IlyaFaer]

One system test create_instance failed with 429 Project 1065521786570 cannot add 1 nodes in region us-central1. Doesn't seem to be related.

[IlyaFaer]

Hm-m, it looks like this ResourceExhausted error became permanent. Maybe it'll be better to move DB API system tests to the original test_system.py file and use one instance for all of the system tests?

[larkee]

Hm-m, it looks like this ResourceExhausted error became permanent. Maybe it'll be better to move DB API system tests to the original test_system.py file and use one instance for all of the system tests?

The issue is test instances failing to be deleted for some runs. Manually deleting instances from the test project can resolve this temporarily. For a more long term solution, see #190

[c24t]

LGTM, let's get a green system test build.