[ENH] Default list_setups to dataframe

[arcwiser]

Metadata

• Reference Issue: Fixes Default output_format to "dataframe" #1115
• New Tests Added: Yes
• Documentation Updated: Yes (API docstring)
• Change Log Entry: Default list_setups to DataFrame output

Details

list_setups was the remaining listing API whose default output was not a pandas DataFrame. This changes its default from "object" to "dataframe" while preserving explicit output_format="object" support for callers that need OpenMLSetup instances.

The DataFrame construction now declares its columns so an empty server response returns an empty DataFrame with the same setup_id index and flow_id/parameters columns as a populated response.

Tests cover populated and empty default results without requiring a server. Existing integration coverage now verifies the DataFrame default and the explicit object compatibility path.

Tested on Windows with Python 3.10:

• pytest tests/test_setups/test_setup_functions.py::test_list_setups_defaults_to_dataframe -q (2 passed)
• pytest tests/test_setups/test_setup_functions.py -m "not production_server and not test_server" -q (2 passed, 10 deselected)
• pytest tests/test_setups/test_setup_functions.py::TestSetupFunctions::test_list_setups_output_format -q against the production OpenML API (1 passed)
• pre-commit run --files openml/setups/functions.py tests/test_setups/test_setup_functions.py (all hooks passed)
• git diff --check upstream/main HEAD

AI-assisted: yes. The contributor reviewed and is responsible for the submitted changes.

[L-Agbaria]

I would personally also prefer if it first introduced a warning regarding future change and conveniently switched "object" to "dict", however it is the last step of a larger change.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 53.68%. Comparing base (0a44155) to head (33803db).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1769   +/-   ##
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  Coverage   53.68%   53.68%           
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  Files          63       63           
  Lines        5251     5251           
=======================================
  Hits         2819     2819           
  Misses       2432     2432           

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