Add itemsgetter, an itemgetter with consistent return type

dwave/inspector/utils.py

@@ -0,0 +1,39 @@
+# Copyright 2020 D-Wave Systems Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+import operator
+
+__all__ = [
+    'itemsgetter',
+]
+
+logger = logging.getLogger(__name__)
+
+
+def itemsgetter(*items):
+    """Variant of :func:`operator.itemgetter` that returns a callable that
+    always returns a tuple, even when called with one argument. This is to make
+    the result type consistent, regardless of input.
+    """
+
+    if len(items) == 1:
+        item = items[0]
+        def f(obj):
+            return (obj[item], )
+
+    else:
+        f = operator.itemgetter(*items)
+
+    return f

tests/test_utils.py

@@ -0,0 +1,38 @@
+# Copyright 2020 D-Wave Systems Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+
+from dwave.inspector.utils import itemsgetter
+
+
+class TestItemsgetter(unittest.TestCase):
+
+    def test_nil(self):
+        with self.assertRaises(TypeError):
+            itemsgetter()
+
+    def test_one(self):
+        obj = list(range(3))
+        f = itemsgetter(1)
+
+        self.assertTrue(callable(f))
+        self.assertEqual(f(obj), (obj[1], ))
+
+    def test_multi(self):
+        obj = list(range(3))
+        f = itemsgetter(0, 2)
+
+        self.assertTrue(callable(f))
+        self.assertEqual(f(obj), (obj[0], obj[2]))