docs: add sample for update transfer config

[HemangChothani]

Fixes #9

[plamut]

I think it's fine.

I added a few comments, but later realized this was just the existing code being moved. If you think they are out of scope and/or too much work, we can ignore them in this PR.

[plamut]

What if the environment variable is not set, e.g. when running the tests locally?

If a test cannot proceed without this value, it would IMO make sense to raise a more informative exception than KeyError.

[HemangChothani]

Before this file environment_variables used in samples/nox.py file, so need to handle there, here i can't edit nox.py file.

python-bigquery-datatransfer/samples/noxfile.py

Lines 67 to 74 in 3c16677

	def get_pytest_env_vars():
	"""Returns a dict for pytest invocation."""
	ret = {}
	# Override the GCLOUD_PROJECT and the alias.
	env_key = TEST_CONFIG['gcloud_project_env']
	# This should error out if not set.
	ret['GOOGLE_CLOUD_PROJECT'] = os.environ[env_key]

[HemangChothani]

Here is the file where we need to change the template format: https://github.com/googleapis/synthtool/blob/master/synthtool/gcp/templates/python_samples/noxfile.py.j2

[plamut]

What about other random errors such as a temporary network timeout or something?

If deleting a resource fails, we would still want to proceed and delete the others, especially if the initial error is transient is is less likely to affect other deletion attempts.

[HemangChothani]

Added else here so all other exception pass here. so every other delete operation will proceed.

[plamut]

@HemangChothani This extra else has no effect here, since it's executed when no exception is raised.

Did you actually mean the following or do I misunderstand the comment?

for resource_name in doomed:
    try:
        # delete resource...
    except Exception:
        pass  # ignore errors

P.S.: If the coverage check complains, a pragma: NO COVER comment should be also added.

[HemangChothani]

@plamut Yes, i will open a separate PR for the comments as don't want to mix-up here.

[plamut]

@HemangChothani That sounds good, thanks.

[HemangChothani]

@plamut Sorry for the noise, but as this branch is didn't merged till now so have push some recommended changes.

[plamut]

@HemangChothani That's OK, please just see the new remark about error catching, thanks!