From 2c25c23be5516934341d4b821239734911517402 Mon Sep 17 00:00:00 2001
From: "Micah D. Gale" <micah.gale@inl.gov>
Date: Tue, 10 Sep 2024 07:21:52 -0500
Subject: [PATCH 1/4] Made tests stricter to only insert once.

---
 tests/test_numbered_collection.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tests/test_numbered_collection.py b/tests/test_numbered_collection.py
index f88cf831..1a6bd36d 100644
--- a/tests/test_numbered_collection.py
+++ b/tests/test_numbered_collection.py
@@ -317,11 +317,13 @@ def test_data_append(cp_simple_problem):
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
     # trigger getting data_inputs end
     prob.materials.clear()
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
     prob.data_inputs.clear()
     prob.materials._last_index = None
     new_mat = copy.deepcopy(next(iter(prob.materials)))
@@ -329,6 +331,7 @@ def test_data_append(cp_simple_problem):
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
     # trigger getting index of last material
     prob.materials._last_index = None
     new_mat = copy.deepcopy(next(iter(prob.materials)))

From d14d96daa09b1a4fd09576ce9f485179f16b2165 Mon Sep 17 00:00:00 2001
From: "Micah D. Gale" <micah.gale@inl.gov>
Date: Tue, 10 Sep 2024 07:22:15 -0500
Subject: [PATCH 2/4] Replicated error #516.

---
 tests/test_numbered_collection.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tests/test_numbered_collection.py b/tests/test_numbered_collection.py
index 1a6bd36d..d5a43f9e 100644
--- a/tests/test_numbered_collection.py
+++ b/tests/test_numbered_collection.py
@@ -339,6 +339,16 @@ def test_data_append(cp_simple_problem):
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
+
+
+def test_data_append_renumber(cp_simple_problem):
+    prob = cp_simple_problem
+    new_mat = copy.deepcopy(next(iter(prob.materials)))
+    prob.materials.append_renumber(new_mat)
+    assert new_mat in prob.materials
+    assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
 
 
 def test_data_remove(cp_simple_problem):

From 8b50e68e69cf5b8499cde1004c832cb287144d64 Mon Sep 17 00:00:00 2001
From: "Micah D. Gale" <micah.gale@inl.gov>
Date: Tue, 10 Sep 2024 07:26:15 -0500
Subject: [PATCH 3/4] Changed order of appending to allow failure first.

---
 montepy/numbered_object_collection.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/montepy/numbered_object_collection.py b/montepy/numbered_object_collection.py
index e542c82e..bbbd49d3 100644
--- a/montepy/numbered_object_collection.py
+++ b/montepy/numbered_object_collection.py
@@ -439,6 +439,7 @@ def append(self, obj, insert_in_data=True):
         :type insert_in_data: bool
         :raises NumberConflictError: if this object has a number that is already in use.
         """
+        super().append(obj)
         if self._problem:
             if self._last_index:
                 index = self._last_index
@@ -452,7 +453,6 @@ def append(self, obj, insert_in_data=True):
             if insert_in_data:
                 self._problem.data_inputs.insert(index + 1, obj)
             self._last_index = index + 1
-        super().append(obj)
 
     def __delitem__(self, idx):
         if not isinstance(idx, int):

From d393950b568b80d5feb1cf3a33ea1fa0571b80d9 Mon Sep 17 00:00:00 2001
From: "Micah D. Gale" <micah.gale@inl.gov>
Date: Tue, 10 Sep 2024 07:30:27 -0500
Subject: [PATCH 4/4] Updated changelog with #516.

---
 doc/source/changelog.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index 530c536c..89e89561 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -4,6 +4,10 @@ MontePy Changelog
 #Next Version#
 --------------
 
+**Bug Fixes**
+
+* Fixed a bug where ``problem.materials.append_renumber`` would double add a material to ``problem.data_inputs`` (:issue:`516`).
+
 **Performance Improvement**
 
 * Fixed method of linking ``Material`` to ``ThermalScattering`` objects, avoiding a very expensive O(N:sup:`2`) (:issue:`510`).