support container client and blob client for azure blob storage

[cbare]

Support ContainerClient and BlobClient in Azure storage

Support use of ContainerClient and BlobClient to access blobs in Azure storage in addition to existing support for BlobServiceClient. Overloads transport_params['client'] to accept any of the three types of clients supported by Azure storage, for example:

transport_params = {
    'client': ContainerClient.from_container_url(container_sas_url),
}

with smart_open.open('azure://path/to/blob', mode='wb', transport_parameters=transport_parameters) as fout:
   fout.write(data)

Motivation

This allows for a least-privilege approach. You can access azure storage with a SAS URL scoped down to a specific container or blob, rather having the full run of the storage account.

- Fixes #651 

Tests

in smart_open/tests/test_azure.py

• test_read_container_client
• test_read_blob_client
• test_write_container_client

[cbare]

Ah flake8, my old friend. Apparently, flake8 takes offense at long lines caused by the type annotations. I added a type alias to resolve that. This introduces the first use of import from typing and modern type annotation syntax, so far as I could tell. Does that impact support for older versions of Python?

[cbare]

@mpenkov mind approving the CICD? Let me know what you think of the way I did the type annotations. I can change if a different way is better. Thanks!

[mpenkov]

Sorry, I've been busy with gensim and other projects this week. I'll try to look at this more closely next week. Thank you for your efforts and your patience!

[cbare]

I don't understand why that test is failing with this NameError during register_transport('smart_open.azure'). Somehow importlib doesn't like my type alias, apparently.

smart_open/azure.py:46: in <module>
    azure.storage.blob.BlobServiceClient,
E   NameError: name 'azure' is not defined

Going back to using the Union in "# type:" comments, plus tagging those lines with "# noqa" seems to fix the above error and also appease flake8. The noqa bit might cause a type-checker some grief, if one where to be run, but Visual Code seems not to mind.

[mpenkov]

fixes #651

[mpenkov]

Somehow importlib doesn't like my type alias, apparently.

Could be because of relative import (azure.blah vs smart_open.azure.blah) but I can't be sure atm. We don't have explicit type annotations right now (but we may in the future) so your type annotations are fine as comments for now.

[mpenkov]

Looks like tests are failing for an unrelated reason. I'll try to investigate over the weekend.

[mpenkov]

OK, I finally got around to investigating this. The parameterizedtestcase package was misbehaving. I got rid of it, because it wasn't strictly necessary. I'll wait for the CI to complete and then continue reviewing this PR. Thanks for your patience!

[mpenkov]

OK, looks good to me. Thank you!