Backport PR #37801 on branch 1.1.x: REGR: SeriesGroupBy where index has a tuple name fails (#37829)

Co-authored-by: Richard Shadrach <45562402+rhshadrach@users.noreply.github.com>

Author: simonjayhawkins

doc/source/whatsnew/v1.1.5.rst

@@ -15,6 +15,7 @@ including other versions of pandas.
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
 - Regression in addition of a timedelta-like scalar to a :class:`DatetimeIndex` raising incorrectly (:issue:`37295`)
+- Fixed regression in :meth:`Series.groupby` raising when the :class:`Index` of the :class:`Series` had a tuple as its name (:issue:`37755`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/core/series.py

@@ -889,7 +889,7 @@ def __getitem__(self, key):
 
  return result
 
- except KeyError:
+ except (KeyError, TypeError):
  if isinstance(key, tuple) and isinstance(self.index, MultiIndex):
  # We still have the corner case where a tuple is a key
  # in the first level of our MultiIndex
@@ -953,7 +953,7 @@ def _get_values_tuple(self, key):
  return result
 
  if not isinstance(self.index, MultiIndex):
- raise ValueError("key of type tuple not found and not a MultiIndex")
+ raise KeyError("key of type tuple not found and not a MultiIndex")
 
  # If key is contained, would have returned by now
  indexer, new_index = self.index.get_loc_level(key)
@@ -1009,7 +1009,7 @@ def __setitem__(self, key, value):
 
  except TypeError as err:
  if isinstance(key, tuple) and not isinstance(self.index, MultiIndex):
- raise ValueError(
+ raise KeyError(
  "key of type tuple not found and not a MultiIndex"
  ) from err
 

pandas/tests/groupby/test_groupby.py

@@ -2055,3 +2055,13 @@ def test_groups_repr_truncates(max_seq_items, expected):
 
  result = df.groupby(np.array(df.a)).groups.__repr__()
  assert result == expected
+
+
+def test_groupby_series_with_tuple_name():
+ # GH 37755
+ ser = Series([1, 2, 3, 4], index=[1, 1, 2, 2], name=("a", "a"))
+ ser.index.name = ("b", "b")
+ result = ser.groupby(level=0).last()
+ expected = Series([2, 4], index=[1, 2], name=("a", "a"))
+ expected.index.name = ("b", "b")
+ tm.assert_series_equal(result, expected)

pandas/tests/series/indexing/test_indexing.py

@@ -387,9 +387,9 @@ def test_2d_to_1d_assignment_raises():
 def test_basic_getitem_setitem_corner(datetime_series):
  # invalid tuples, e.g. td.ts[:, None] vs. td.ts[:, 2]
  msg = "key of type tuple not found and not a MultiIndex"
- with pytest.raises(ValueError, match=msg):
+ with pytest.raises(KeyError, match=msg):
  datetime_series[:, 2]
- with pytest.raises(ValueError, match=msg):
+ with pytest.raises(KeyError, match=msg):
  datetime_series[:, 2] = 2
 
  # weird lists. [slice(0, 5)] will work but not two slices