rusackas opened a new pull request, #41881:
URL: https://github.com/apache/superset/pull/41881
### SUMMARY
`Python-Unit` has been intermittently failing on master's `unit-tests
(previous)` job (Python 3.10) since ~2026-07-07T16:51, with:
```
AttributeError: <function list_metrics at 0x...> does not have the attribute
'DatasetDAO'
```
Root cause: `superset/mcp_service/semantic_layer/tool/__init__.py`
re-exports the `list_metrics` function under the same name as its defining
submodule:
```python
from superset.mcp_service.semantic_layer.tool.list_metrics import (
list_metrics,
)
```
This overwrites the `tool.list_metrics` package attribute (originally set to
the submodule by Python's import machinery) with the function object.
`tests/unit_tests/mcp_service/semantic_layer/tool/test_list_metrics.py` patches
`DatasetDAO`/`SemanticViewDAO`/`db` via the dotted string
`"superset.mcp_service.semantic_layer.tool.list_metrics.DatasetDAO"`. On Python
3.10, `unittest.mock`'s target resolution (`_importer`) walks the dotted path
via plain `getattr`, so it resolves `tool.list_metrics` to the shadowed
function instead of the submodule, then fails looking up `DatasetDAO` on it.
This was fixed in a later CPython version (mock's resolution now prefers
importing the submodule directly), so the bug only reproduces on 3.10 — hence
the flip-flopping pass/fail pattern across the Python version matrix.
Confirmed with a minimal repro locally: fails identically on Python 3.10.14,
passes on 3.13.0a5.
The fix switches the affected patches to `patch.object(list_metrics_module,
"X")` against the module reference this file already imports at the top
(`importlib.import_module(...)`) — the same pattern this file already uses for
`user_can_view_data_model_metadata`. This sidesteps the ambiguous string
resolution entirely rather than depending on Python-version-specific mock
internals.
Checked sibling test files in the same package (`test_get_table.py`,
`test_get_compatible_metrics.py`, `test_get_compatible_dimensions.py`) for the
same footgun — they patch DAOs at their defining module (e.g.
`superset.daos.dataset.DatasetDAO`) rather than through the re-exporting
package, so they're unaffected.
### TESTING INSTRUCTIONS
On Python 3.10:
```
pytest tests/unit_tests/mcp_service/semantic_layer/tool/test_list_metrics.py
-v
```
Previously failed 6 tests with the `AttributeError` above; should now pass.
`pre-commit run --files
tests/unit_tests/mcp_service/semantic_layer/tool/test_list_metrics.py` passes
clean (ruff, mypy).
### ADDITIONAL INFORMATION
- [ ] Has associated issue:
- [ ] Required feature flags:
- [ ] Changes UI
- [ ] Includes DB Migration
- [ ] Introduces new feature or API
- [ ] Removes existing feature or API
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