[thodson-usgs]

Summary

pandas 3.1.0 (released 10/2026) deprecates set_index(..., inplace=True) with a Pandas4Warning, which subclasses DeprecationWarning. nwis.format_response calls it for every frame with a datetime column, so the 3.13 and 3.14 test jobs on main fail test_nested_calls_emit_one_warning on the second warning. The 3.10 jobs install pandas 2.x and pass.

 df = df.copy(deep=False)
-df.set_index(keys, inplace=True)
+levels = [df.pop(key) for key in keys]
+df.index = (
+    pd.MultiIndex.from_arrays(levels) if len(levels) > 1 else pd.Index(levels[0])
+)

The in-place call was deliberate: on pandas 2 with copy-on-write off, set_index without it copies every column. Popping the key columns off the shallow copy is what set_index(inplace=True) does internally, so that property is kept without the deprecated keyword.

Evidence

• Before: pandas 3.1.0, Python 3.13 (as in CI, e.g. run 40888458898):

  FAILED tests/nwis_test.py::TestDeprecationWarnings::test_nested_calls_emit_one_warning - assert 2 == 1
  Pandas4Warning: The inplace keyword in DataFrame.set_index is deprecated ... (PDEP-8)
  

  After: full offline suite, 1757 passed, no Pandas4Warning, on pandas 3.1.0 (Python 3.13), 2.3.3 (3.12) and 3.0.5 (3.12).
• format_response before and after, on pandas 3.1.0 and 2.3.3 (single-site, multi-site, multi_index=False, GeoDataFrame, string datetimes, peaks):

  frames and indexes: identical (assert_frame_equal, check_exact; assert_index_equal, exact)
  warnings:           pandas 3.1: 2 Pandas4Warning -> none;  pandas 2.3: none -> none
  peak heap / frame:  pandas 3.1: 0.83 -> 0.83;              pandas 2.3: 1.12 -> 1.12
  

Merge Danger

Door: two-way

Blast Radius: none

format_response returns the same frames. The only visible difference is that pandas 3.1 users no longer see the warning.

🤖 Generated with Claude Code