ENH: (Issue #1234) add exception when user tries to create more than one persistent or ephemeral client.

[vaughanlove]

ref: #1234

Description of changes

Summarize the changes made by this PR.

• added @once decorator to PersistentClient() and EphemeralClient() in chromadb/init.py.
• added once() in chromadb.utils that raises a RuntimeError when user tries to instantiate more than one persistent or ephemeral client.

Test plan

How are these changes tested?

• added 4 tests in chromadb/test/test_client.py. Two tests to test if the error is raised, two tests to see if a client can be instantiated after a previous client had been instantiated, destroyed, and garbage collected.
• Tests pass locally with pytest for python

Documentation Changes

small change to usage-guide.md
https://github.com/vaughanlove/docs/tree/update

Side note:
This is my first open-source contribution. I want to learn and improve, any advice appreciated.

[github-actions]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readbility, Modularity, Intuitiveness)

[HammadB]

Hi! Thanks for doing this!

I think we are going to go with #1244 - which adds a mechanism which allows you to create multiple clients, rather than prevent it. As its a very common need.

[vaughanlove]

Hi! Thanks for doing this!

I think we are going to go with #1244 - which adds a mechanism which allows you to create multiple clients, rather than prevent it. As its a very common need.

No worries!

Yeah, I agree that is a better way to go.