Fix groupby.get_group with length-1 tuple with list-like grouper (#17216

)

closes #17187

Adds similar logic as implemented in pandas: https://github.com/pandas-dev/pandas/blob/main/pandas/core/groupby/groupby.py#L751-L758

Authors:
  - Matthew Roeschke (https://github.com/mroeschke)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: #17216

python/cudf/cudf/core/groupby/groupby.py

@@ -481,6 +481,11 @@ def get_group(self, name, obj=None):
                 "instead of ``gb.get_group(name, obj=df)``.",
                 FutureWarning,
             )
+        if is_list_like(self._by):
+            if isinstance(name, tuple) and len(name) == 1:
+                name = name[0]
+            else:
+                raise KeyError(name)
         return obj.iloc[self.indices[name]]
 
     @_performance_tracking

python/cudf/cudf/tests/test_groupby.py

@@ -4059,3 +4059,19 @@ def test_ndim():
     pgb = pser.groupby([0, 0, 1])
     ggb = gser.groupby(cudf.Series([0, 0, 1]))
     assert pgb.ndim == ggb.ndim
+
+
+@pytest.mark.skipif(
+    not PANDAS_GE_220, reason="pandas behavior applicable in >=2.2"
+)
+def test_get_group_list_like():
+    df = cudf.DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    result = df.groupby(["a"]).get_group((1,))
+    expected = df.to_pandas().groupby(["a"]).get_group((1,))
+    assert_eq(result, expected)
+
+    with pytest.raises(KeyError):
+        df.groupby(["a"]).get_group((1, 2))
+
+    with pytest.raises(KeyError):
+        df.groupby(["a"]).get_group([1])