Fix indexing syntax not valid for Python<3.11. (#185)

* Fix indexing not working with Python 3.10.

* Changenote.

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: pp-mo

docs/changelog_fragments/183.bug.rst

@@ -0,0 +1 @@
+Made indexing work with Python v3.10.

lib/ncdata/_core.py

@@ -500,8 +500,12 @@ def slicer(self, *dim_names):
 
         return Slicer(self, *dim_names)
 
-    def __getitem__(self, keys):  # noqa: D105
-        return self.slicer()[*keys]
+    def __getitem__(self, indices):  # noqa: D105
+        # N.B. Python [,,] syntax ensures there is only ever one argument,
+        #  either a single key or a tuple :
+        #    : [x] --> keys == x
+        #    : [x, y, ...] --> keys == (x, y, ...)
+        return self.slicer().__getitem__(indices)
 
     # Define equality in terms of dataset comparison utility
     def __eq__(self, other):  # noqa: D105

tests/unit/core/test_NcData.py

@@ -3,6 +3,7 @@
 There is almost no behaviour, but we can test some constructor usages.
 """
 
+import pytest
 from ncdata import NcData, NcDimension, NcVariable
 
 
@@ -99,17 +100,28 @@ def test(self, mocker):
 
 class Test_NcVariable_getitem:
     # check that data[*keys] calls data.slicer[*keys]
-    def test(self, mocker):
+    @pytest.mark.parametrize(
+        "multiple_indices", [False, True], ids=["oneIndex", "multiIndex"]
+    )
+    def test(self, mocker, multiple_indices):
         from ncdata.utils import Slicer
 
         ncdata1 = NcData()
 
-        dim_keys = (1, 2, 3)  # N.B. not actually acceptable for a real usage
         mock_slicer = mocker.MagicMock(spec=Slicer)
         called = mocker.patch(
             "ncdata._core.NcData.slicer", return_value=mock_slicer
         )
-        result = ncdata1[*dim_keys]
+        if multiple_indices:
+            # Index with multiple keys, which should be passed as a tuple
+            # Slightly awkward code, because the "[*keys]" syntax is only valid from
+            #  Python >=3.11
+            result = ncdata1[1, 2, 3]
+            dim_keys = (1, 2, 3)
+        else:
+            # Index with a single key: should be passed as-is
+            dim_keys = slice(0, 3)
+            result = ncdata1[dim_keys]
 
         assert called.call_args_list == [mocker.call()]
         assert mock_slicer.__getitem__.call_args_list == [