From b7d132dc72fb80347242bb50b5c84e6df9991d00 Mon Sep 17 00:00:00 2001
From: John Siirola <jsiirola@users.noreply.github.com>
Date: Thu, 9 Mar 2023 09:11:17 -0700
Subject: [PATCH 1/3] Correct indexing by unhashable objects convertable to
 tuple

---
 pyomo/core/base/indexed_component.py | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/pyomo/core/base/indexed_component.py b/pyomo/core/base/indexed_component.py
index 38c10190114..eac2effbc4e 100644
--- a/pyomo/core/base/indexed_component.py
+++ b/pyomo/core/base/indexed_component.py
@@ -805,7 +805,6 @@ def _processUnhashableIndex(self, idx):
         fixed = {}
         sliced = {}
         ellipsis = None
-        _found_numeric = False
         #
         # Setup the slice template (in fixed)
         #
@@ -844,8 +843,6 @@ def _processUnhashableIndex(self, idx):
                 # should raise a TemplateExpressionError
                 try:
                     val = EXPR.evaluate_expression(val, constant=True)
-                    _found_numeric = True
-
                 except TemplateExpressionError:
                     #
                     # The index is a template expression, so return the
@@ -937,7 +934,7 @@ def _processUnhashableIndex(self, idx):
                     IndexedComponent_slice._getitem_args_to_str(list(idx)),
                     self.name, set_dim, slice_dim))
             return IndexedComponent_slice(self, fixed, sliced, ellipsis)
-        elif _found_numeric:
+        elif len(idx) == len(fixed):
             if len(idx) == 1:
                 return fixed[0]
             else:

From 978aac9ccf91e23e55bfeefa723169bdb9405a9f Mon Sep 17 00:00:00 2001
From: John Siirola <jsiirola@users.noreply.github.com>
Date: Thu, 9 Mar 2023 09:11:40 -0700
Subject: [PATCH 2/3] Add tests for indexing by list

---
 pyomo/core/tests/unit/test_indexed.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/pyomo/core/tests/unit/test_indexed.py b/pyomo/core/tests/unit/test_indexed.py
index 7308c908d3d..f45a5dd999e 100644
--- a/pyomo/core/tests/unit/test_indexed.py
+++ b/pyomo/core/tests/unit/test_indexed.py
@@ -223,9 +223,26 @@ def test_index_var_by_tuple_with_variables(self):
     def test_index_by_unhashable_type(self):
         m = ConcreteModel()
         m.x = Var([1,2,3], initialize=lambda m,x: 2*x)
+        # Indexing by a dict raises an error
         self.assertRaisesRegex(
             TypeError, '.*',
             m.x.__getitem__, {})
+        # Indexing by lists works...
+        # ... scalar
+        self.assertIs(m.x[[1]], m.x[1])
+        # ... "tuple"
+        m.y = Var([(1, 1), (1, 2)])
+        self.assertIs(m.y[[1, 1]], m.y[1, 1])
+        m.y[[1, 2]] = 5
+        y12 = m.y[[1, 2]]
+        self.assertEqual(y12.value, 5)
+        m.y[[1, 2]] = 15
+        self.assertIs(y12, m.y[[1, 2]])
+        self.assertEqual(y12.value, 15)
+        with self.assertRaisesRegex(
+                KeyError, r"Index '\(2, 2\)' is not valid for indexed component 'y'"):
+            m.y[[2, 2]] = 5
+
 
     def test_ordered_keys(self):
         m = ConcreteModel()

From bdbc14ef8762d732c2922583093466b44667203c Mon Sep 17 00:00:00 2001
From: John Siirola <jsiirola@users.noreply.github.com>
Date: Thu, 9 Mar 2023 09:11:55 -0700
Subject: [PATCH 3/3] Improve developer error message information

---
 pyomo/core/base/indexed_component.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pyomo/core/base/indexed_component.py b/pyomo/core/base/indexed_component.py
index eac2effbc4e..01bd6f5fd07 100644
--- a/pyomo/core/base/indexed_component.py
+++ b/pyomo/core/base/indexed_component.py
@@ -802,6 +802,7 @@ def _processUnhashableIndex(self, idx):
         # Iterate through the index and look for slices and constant
         # components
         #
+        orig_idx = idx
         fixed = {}
         sliced = {}
         ellipsis = None
@@ -942,7 +943,7 @@ def _processUnhashableIndex(self, idx):
         else:
             raise DeveloperError(
                 "Unknown problem encountered when trying to retrieve "
-                "index for component %s" % (self.name,) )
+                f"index '{orig_idx}' for component '{self.name}'")
 
     def _getitem_when_not_present(self, index):
         """Returns/initializes a value when the index is not in the _data dict.