Do not touch botocore unless it is installed

[ddelange]

Title

Raise a proper S3 import exception (leftover from #785).

Motivation

Leftover from #785, not raising the proper Exception anymore:

  File "/usr/share/python3/app/lib/python3.11/site-packages/smart_open/s3.py", line 121, in <module>
    RETRY = Retry()
            ^^^^^^^
  File "/usr/share/python3/app/lib/python3.11/site-packages/smart_open/s3.py", line 86, in __init__
    self.exceptions: List[Exception] = [botocore.exceptions.EndpointConnectionError]
                                        ^^^^^^^^
NameError: name 'botocore' is not defined

Tests

Work in progress

Checklist

Before you create the PR, please make sure you have:

• Picked a concise, informative and complete title
• Clearly explained the motivation behind the PR
• Linked to any existing issues that your PR will be solving
• Included tests for any new functionality
• Checked that all unit tests pass

Workflow

[ddelange]

cc @mpenkov this error was raised when importing smart_open on a smart_open[azure] container.

[ddelange]

hmm, now we're getting

smart_open/transport.py:22: in <module>
    _REGISTRY = {NO_SCHEME: smart_open.local_file}
E   AttributeError: partially initialized module 'smart_open' has no attribute 'local_file' (most likely due to a circular import)

What would be the proper fix?

edit: 252430c

[ddelange]

is there a point in time where we can test import smart_open before any optional deps are installed? to catch this case?

edit: 947bbe0

[mpenkov]

Fixes #804

[mpenkov]

Thank you @ddelange !

[ddelange]

thanks too for the quick action!