From 83b61f7db0491fca9daf9e7d0228df434761e0d5 Mon Sep 17 00:00:00 2001
From: DIGVIJAY <144053736+digvijay-y@users.noreply.github.com>
Date: Wed, 17 Dec 2025 17:22:47 +0000
Subject: [PATCH 1/5] weakref

---
 demo/_config.py                       |  2 ++
 montepy/cell.py                       |  7 +++++
 montepy/mcnp_object.py                | 11 ++++++-
 montepy/numbered_mcnp_object.py       | 42 +++++++++++++++++----------
 montepy/numbered_object_collection.py | 26 ++++++++++++++---
 montepy/surfaces/half_space.py        | 29 ++++++++++++++++++
 tests/test_numbered_collection.py     |  2 ++
 7 files changed, 98 insertions(+), 21 deletions(-)

diff --git a/demo/_config.py b/demo/_config.py
index bdd243f4..355ad7d8 100644
--- a/demo/_config.py
+++ b/demo/_config.py
@@ -8,7 +8,9 @@
 def IFrame(src, width=X_RES, height=Y_RES, extras=None, **kwargs):
     return _iframe(src, width, height, extras, **kwargs)
 
+
 def install_montepy():
     if "pyodide" in sys.modules:
         import piplite
+
         piplite.install("montepy")
diff --git a/montepy/cell.py b/montepy/cell.py
index 429b32d7..297d3ea9 100644
--- a/montepy/cell.py
+++ b/montepy/cell.py
@@ -922,6 +922,13 @@ def num(obj):
         for key in keys:
             attr = getattr(self, key)
             setattr(result, key, copy.deepcopy(attr, memo))
+        # Clear weakrefs so the cloned cell isn't linked to original collection/problem
+        # This prevents number conflict checks against the original collection
+        result._collection_ref = None
+        result._problem_ref = None
+        # Update the geometry's _cell references to point to result, not the deepcopied intermediate
+        if result._geometry is not None:
+            result._geometry._set_cell(result)
         # copy geometry
         for special in special_keys:
             new_objs = []
diff --git a/montepy/mcnp_object.py b/montepy/mcnp_object.py
index 72943faf..a9b00280 100644
--- a/montepy/mcnp_object.py
+++ b/montepy/mcnp_object.py
@@ -107,6 +107,7 @@ def __init__(
         except AttributeError:
             self._BLOCK_TYPE = montepy.input_parser.block_type.BlockType.DATA
         self._problem_ref = None
+        self._collection_ref = None
         self._parameters = ParametersNode()
         self._input = None
         if input:
@@ -225,6 +226,13 @@ def _update_values(self):
         """
         pass
 
+    @property
+    def _collection(self):
+        """Returns the parent collection this object belongs to, if any."""
+        if self._collection_ref is not None:
+            return self._collection_ref()
+        return None
+
     def format_for_mcnp_input(self, mcnp_version: tuple[int]) -> list[str]:
         """Creates a list of strings representing this MCNP_Object that can be
         written to file.
@@ -490,7 +498,7 @@ def _grab_beginning_comment(self, padding: list[PaddingNode], last_obj=None):
 
     def __getstate__(self):
         state = self.__dict__.copy()
-        bad_keys = {"_problem_ref", "_parser"}
+        bad_keys = {"_problem_ref", "_collection_ref", "_parser"}
         for key in bad_keys:
             if key in state:
                 del state[key]
@@ -498,6 +506,7 @@ def __getstate__(self):
 
     def __setstate__(self, crunchy_data):
         crunchy_data["_problem_ref"] = None
+        crunchy_data["_collection_ref"] = None
         self.__dict__.update(crunchy_data)
 
     def clone(self) -> montepy.mcnp_object.MCNP_Object:
diff --git a/montepy/numbered_mcnp_object.py b/montepy/numbered_mcnp_object.py
index 6137b1ce..043b42f9 100644
--- a/montepy/numbered_mcnp_object.py
+++ b/montepy/numbered_mcnp_object.py
@@ -5,6 +5,7 @@
 import itertools
 from typing import Union
 from numbers import Integral
+import weakref
 
 from montepy.mcnp_object import MCNP_Object, InitInput
 import montepy
@@ -14,22 +15,31 @@
 def _number_validator(self, number):
     if number < 0:
         raise ValueError("number must be >= 0")
-    if self._problem:
-        obj_map = montepy.MCNP_Problem._NUMBERED_OBJ_MAP
-        try:
-            collection_type = obj_map[type(self)]
-        except KeyError as e:
-            found = False
-            for obj_class in obj_map:
-                if isinstance(self, obj_class):
-                    collection_type = obj_map[obj_class]
-                    found = True
-                    break
-            if not found:
-                raise e
-        collection = getattr(self._problem, collection_type.__name__.lower())
-        collection.check_number(number)
-        collection._update_number(self.number, number, self)
+
+    # Only validate against collection if linked to a problem
+    if self._problem is not None:
+        if self._collection is not None:
+            collection = self._collection
+        else:
+            # Find collection via _problem
+            obj_map = montepy.MCNP_Problem._NUMBERED_OBJ_MAP
+            collection_type = obj_map.get(type(self))
+
+            if collection_type is None:
+                # Finding via inheritance
+                for obj_class in obj_map:
+                    if isinstance(self, obj_class):
+                        collection_type = obj_map[obj_class]
+                        break
+
+            if collection_type is not None:
+                collection = getattr(self._problem, collection_type.__name__.lower())
+            else:
+                collection = None
+
+        if collection is not None:
+            collection.check_number(number)
+            collection._update_number(self.number, number, self)
 
 
 class Numbered_MCNP_Object(MCNP_Object):
diff --git a/montepy/numbered_object_collection.py b/montepy/numbered_object_collection.py
index 52ceb32f..1d8a087e 100644
--- a/montepy/numbered_object_collection.py
+++ b/montepy/numbered_object_collection.py
@@ -178,6 +178,7 @@ def __init__(
                         )
                     )
                 self.__num_cache[obj.number] = obj
+                obj._collection_ref = weakref.ref(self)
             self._objects = objects
 
     def link_to_problem(self, problem):
@@ -196,8 +197,18 @@ def link_to_problem(self, problem):
             self._problem_ref = None
         else:
             self._problem_ref = weakref.ref(problem)
+        # Rebuild the number cache to ensure it reflects current object numbers
+        # after deepcopy/unpickling when the cache might be stale
+        self.__num_cache.clear()
+        for obj in self._objects:
+            self.__num_cache[obj.number] = obj
         for obj in self:
             obj.link_to_problem(problem)
+            # the _collection_ref that points to the main cells collection.
+            if problem is not None:
+                existing_coll = obj._collection
+                if existing_coll is None or existing_coll._problem is not problem:
+                    obj._collection_ref = weakref.ref(self)
 
     @property
     def _problem(self):
@@ -340,11 +351,15 @@ def extend(self, other_list):
                     "The object in the list {obj} is not of type: {self._obj_class}"
                 )
             if obj.number in nums:
-                raise NumberConflictError(
-                    (
-                        f"When adding to {type(self).__name__} there was a number collision due to "
-                        f"adding {obj} which conflicts with {self[obj.number]}"
+                try:
+                    conflicting_obj = self[obj.number]
+                    conflict_msg = (
+                        f"adding {obj} which conflicts with {conflicting_obj}"
                     )
+                except KeyError:
+                    conflict_msg = f"adding {obj} which conflicts with existing object number {obj.number}"
+                raise NumberConflictError(
+                    f"When adding to {type(self).__name__} there was a number collision due to {conflict_msg}"
                 )
             nums.add(obj.number)
         for obj in other_list:
@@ -496,6 +511,7 @@ def __internal_append(self, obj, **kwargs):
                 )
         self.__num_cache[obj.number] = obj
         self._objects.append(obj)
+        obj._collection_ref = weakref.ref(self)
         self._append_hook(obj, **kwargs)
         if self._problem:
             obj.link_to_problem(self._problem)
@@ -507,6 +523,7 @@ def __internal_delete(self, obj, **kwargs):
         """
         self.__num_cache.pop(obj.number, None)
         self._objects.remove(obj)
+        obj._collection_ref = None
         self._delete_hook(obj, **kwargs)
 
     def add(self, obj: Numbered_MCNP_Object):
@@ -613,6 +630,7 @@ def append_renumber(self, obj, step=1):
         number = obj.number if obj.number > 0 else 1
         if self._problem:
             obj.link_to_problem(self._problem)
+        obj._collection_ref = None
         try:
             self.append(obj)
         except (NumberConflictError, ValueError) as e:
diff --git a/montepy/surfaces/half_space.py b/montepy/surfaces/half_space.py
index 9717b7eb..ee63dcaa 100644
--- a/montepy/surfaces/half_space.py
+++ b/montepy/surfaces/half_space.py
@@ -187,6 +187,22 @@ def update_pointers(self, cells, surfaces, cell):
         if self.right is not None:
             self.right.update_pointers(cells, surfaces, cell)
 
+    def _set_cell(self, cell):
+        """Sets the _cell reference for this HalfSpace and all children.
+
+        This is used during cloning to update the _cell references to point
+        to the cloned cell rather than the original (or a deepcopied intermediate).
+
+        Parameters
+        ----------
+        cell : Cell
+            the cell this HalfSpace should be tied to.
+        """
+        self._cell = cell
+        self.left._set_cell(cell)
+        if self.right is not None:
+            self.right._set_cell(cell)
+
     def _add_new_children_to_cell(self, other):
         """Adds the cells and surfaces from a new tree to this parent cell.
 
@@ -676,6 +692,19 @@ def update_pointers(self, cells, surfaces, cell):
                     "Cell", self._cell.number, "Surface", self._divider
                 )
 
+    def _set_cell(self, cell):
+        """Sets the _cell reference for this UnitHalfSpace.
+
+        This is used during cloning to update the _cell references to point
+        to the cloned cell rather than the original (or a deepcopied intermediate).
+
+        Parameters
+        ----------
+        cell : Cell
+            the cell this UnitHalfSpace should be tied to.
+        """
+        self._cell = cell
+
     def _ensure_has_nodes(self):
         if self.node is None:
             if isinstance(self.divider, Integral):
diff --git a/tests/test_numbered_collection.py b/tests/test_numbered_collection.py
index e5335cd4..1eb7fcde 100644
--- a/tests/test_numbered_collection.py
+++ b/tests/test_numbered_collection.py
@@ -86,6 +86,7 @@ def test_extend(self, cp_simple_problem):
         extender = copy.deepcopy(extender)
         for surf in extender:
             surf._problem = None
+            surf._collection_ref = None
         surfaces[1000].number = 1
         extender[0].number = 1000
         extender[1].number = 70
@@ -161,6 +162,7 @@ def test_append_renumber(self, cp_simple_problem):
             cells.append_renumber(cell, "hi")
         cell = copy.deepcopy(cell)
         cell._problem = None
+        cell._collection_ref = None
         cell.number = 1
         cells.append_renumber(cell)
         assert cell.number == 4

From 3ca4d871177588f34c5da2f50c94466dc03aaec4 Mon Sep 17 00:00:00 2001
From: DIGVIJAY <144053736+digvijay-y@users.noreply.github.com>
Date: Mon, 5 Jan 2026 13:25:27 +0000
Subject: [PATCH 2/5] changes to collection_ref

---
 demo/0_IntroToMontePy.ipynb            |  5 +--
 demo/1_PinCellCorrection_inter.ipynb   |  3 +-
 demo/2_BuildAssembly_inter.ipynb       |  1 +
 demo/3_AddingGuideTubes_inter.ipynb    |  1 +
 demo/4_AxialDiscretize_inter.ipynb     |  1 +
 demo/answers/1_PinCellCorrection.ipynb |  3 +-
 demo/answers/2_BuildAssembly.ipynb     |  3 +-
 demo/answers/3_AddingGuideTubes.ipynb  |  1 +
 demo/answers/4_AxialDiscretize.ipynb   |  1 +
 doc/source/changelog.rst               |  1 +
 montepy/cell.py                        |  3 --
 montepy/mcnp_object.py                 | 11 +------
 montepy/numbered_mcnp_object.py        | 28 +++++++++++++---
 montepy/numbered_object_collection.py  | 45 +++++++++++++++-----------
 montepy/surfaces/half_space.py         | 29 -----------------
 15 files changed, 67 insertions(+), 69 deletions(-)

diff --git a/demo/0_IntroToMontePy.ipynb b/demo/0_IntroToMontePy.ipynb
index 56312f06..c267ce89 100644
--- a/demo/0_IntroToMontePy.ipynb
+++ b/demo/0_IntroToMontePy.ipynb
@@ -228,8 +228,9 @@
    },
    "outputs": [],
    "source": [
-    "#note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
+    "# note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
@@ -428,7 +429,7 @@
    },
    "outputs": [],
    "source": [
-    "#note this %pip is only needed for running in jupyterlite online\n",
+    "# note this %pip is only needed for running in jupyterlite online\n",
     "%pip install ipython\n",
     "from _config import IFrame\n",
     "\n",
diff --git a/demo/1_PinCellCorrection_inter.ipynb b/demo/1_PinCellCorrection_inter.ipynb
index 934ff656..2909c97a 100644
--- a/demo/1_PinCellCorrection_inter.ipynb
+++ b/demo/1_PinCellCorrection_inter.ipynb
@@ -121,8 +121,9 @@
    },
    "outputs": [],
    "source": [
-    "#note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
+    "# note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "# actually needed\n",
diff --git a/demo/2_BuildAssembly_inter.ipynb b/demo/2_BuildAssembly_inter.ipynb
index 89db4008..766331bf 100644
--- a/demo/2_BuildAssembly_inter.ipynb
+++ b/demo/2_BuildAssembly_inter.ipynb
@@ -65,6 +65,7 @@
    "outputs": [],
    "source": [
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
diff --git a/demo/3_AddingGuideTubes_inter.ipynb b/demo/3_AddingGuideTubes_inter.ipynb
index 9be2c4be..dc6af1cb 100644
--- a/demo/3_AddingGuideTubes_inter.ipynb
+++ b/demo/3_AddingGuideTubes_inter.ipynb
@@ -105,6 +105,7 @@
    "outputs": [],
    "source": [
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
diff --git a/demo/4_AxialDiscretize_inter.ipynb b/demo/4_AxialDiscretize_inter.ipynb
index c1cffafa..a0241fb9 100644
--- a/demo/4_AxialDiscretize_inter.ipynb
+++ b/demo/4_AxialDiscretize_inter.ipynb
@@ -71,6 +71,7 @@
    "outputs": [],
    "source": [
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
diff --git a/demo/answers/1_PinCellCorrection.ipynb b/demo/answers/1_PinCellCorrection.ipynb
index edc645f7..7485e91b 100644
--- a/demo/answers/1_PinCellCorrection.ipynb
+++ b/demo/answers/1_PinCellCorrection.ipynb
@@ -120,8 +120,9 @@
    },
    "outputs": [],
    "source": [
-    "#note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
+    "# note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "# actually needed\n",
diff --git a/demo/answers/2_BuildAssembly.ipynb b/demo/answers/2_BuildAssembly.ipynb
index b651fa4f..ddb3e536 100644
--- a/demo/answers/2_BuildAssembly.ipynb
+++ b/demo/answers/2_BuildAssembly.ipynb
@@ -64,8 +64,9 @@
    },
    "outputs": [],
    "source": [
-    "#note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
+    "# note this install_montepy is only necessary for jupyterlite; You don't need to use it locally\n",
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
diff --git a/demo/answers/3_AddingGuideTubes.ipynb b/demo/answers/3_AddingGuideTubes.ipynb
index f21e9bfa..bcb5c3ab 100644
--- a/demo/answers/3_AddingGuideTubes.ipynb
+++ b/demo/answers/3_AddingGuideTubes.ipynb
@@ -104,6 +104,7 @@
    "outputs": [],
    "source": [
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
diff --git a/demo/answers/4_AxialDiscretize.ipynb b/demo/answers/4_AxialDiscretize.ipynb
index a70f87f7..8ffe339d 100644
--- a/demo/answers/4_AxialDiscretize.ipynb
+++ b/demo/answers/4_AxialDiscretize.ipynb
@@ -71,6 +71,7 @@
    "outputs": [],
    "source": [
     "from _config import install_montepy\n",
+    "\n",
     "install_montepy()\n",
     "\n",
     "import montepy\n",
diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index 3b805cbd..47e5ab58 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -14,6 +14,7 @@ MontePy Changelog
 
 **Features Added**
 
+* Implement _collection_ref to link objects to their NumberedObjectCollection parent (:issue:`867`).
 * Added checking for additional input after the ``data`` block, and raising a warning if it exists (:issue:`525`).
 * Allow multiple universe fills to accept 2D MNCP lattices (:issue:`719`).
 * Make ``LatticeType.RECTANGULAR`` and ``LatticeType.HEXAHEDRAL`` synonymous (:issue:`808`).
diff --git a/montepy/cell.py b/montepy/cell.py
index f85e19e9..39095400 100644
--- a/montepy/cell.py
+++ b/montepy/cell.py
@@ -931,9 +931,6 @@ def num(obj):
         # This prevents number conflict checks against the original collection
         result._collection_ref = None
         result._problem_ref = None
-        # Update the geometry's _cell references to point to result, not the deepcopied intermediate
-        if result._geometry is not None:
-            result._geometry._set_cell(result)
         # copy geometry
         for special in special_keys:
             new_objs = []
diff --git a/montepy/mcnp_object.py b/montepy/mcnp_object.py
index a9b00280..72943faf 100644
--- a/montepy/mcnp_object.py
+++ b/montepy/mcnp_object.py
@@ -107,7 +107,6 @@ def __init__(
         except AttributeError:
             self._BLOCK_TYPE = montepy.input_parser.block_type.BlockType.DATA
         self._problem_ref = None
-        self._collection_ref = None
         self._parameters = ParametersNode()
         self._input = None
         if input:
@@ -226,13 +225,6 @@ def _update_values(self):
         """
         pass
 
-    @property
-    def _collection(self):
-        """Returns the parent collection this object belongs to, if any."""
-        if self._collection_ref is not None:
-            return self._collection_ref()
-        return None
-
     def format_for_mcnp_input(self, mcnp_version: tuple[int]) -> list[str]:
         """Creates a list of strings representing this MCNP_Object that can be
         written to file.
@@ -498,7 +490,7 @@ def _grab_beginning_comment(self, padding: list[PaddingNode], last_obj=None):
 
     def __getstate__(self):
         state = self.__dict__.copy()
-        bad_keys = {"_problem_ref", "_collection_ref", "_parser"}
+        bad_keys = {"_problem_ref", "_parser"}
         for key in bad_keys:
             if key in state:
                 del state[key]
@@ -506,7 +498,6 @@ def __getstate__(self):
 
     def __setstate__(self, crunchy_data):
         crunchy_data["_problem_ref"] = None
-        crunchy_data["_collection_ref"] = None
         self.__dict__.update(crunchy_data)
 
     def clone(self) -> montepy.mcnp_object.MCNP_Object:
diff --git a/montepy/numbered_mcnp_object.py b/montepy/numbered_mcnp_object.py
index 043b42f9..94028fad 100644
--- a/montepy/numbered_mcnp_object.py
+++ b/montepy/numbered_mcnp_object.py
@@ -35,11 +35,12 @@ def _number_validator(self, number):
             if collection_type is not None:
                 collection = getattr(self._problem, collection_type.__name__.lower())
             else:
-                collection = None
+                raise TypeError(
+                    f"Could not find collection type for {type(self).__name__} in problem."
+                )
 
-        if collection is not None:
-            collection.check_number(number)
-            collection._update_number(self.number, number, self)
+        collection.check_number(number)
+        collection._update_number(self.number, number, self)
 
 
 class Numbered_MCNP_Object(MCNP_Object):
@@ -69,6 +70,7 @@ def __init__(
             self._number = self._generate_default_node(int, -1)
         super().__init__(input, parser)
         self._load_init_num(number)
+        self._collection_ref = None
 
     def _load_init_num(self, number):
         if number is not None:
@@ -133,6 +135,24 @@ def _add_children_objs(self, problem):
                 except (TypeError, AssertionError):
                     prob_collect.append(child_collect)
 
+    @property
+    def _collection(self):
+        """Returns the parent collection this object belongs to, if any."""
+        if self._collection_ref is not None:
+            return self._collection_ref()
+        return None
+
+    def __getstate__(self):
+        state = super().__getstate__()
+        # Remove _collection_ref weakref as it can't be pickled
+        if "_collection_ref" in state:
+            del state["_collection_ref"]
+        return state
+
+    def __setstate__(self, crunchy_data):
+        crunchy_data["_collection_ref"] = None
+        super().__setstate__(crunchy_data)
+
     def clone(self, starting_number=None, step=None):
         """Create a new independent instance of this object with a new number.
 
diff --git a/montepy/numbered_object_collection.py b/montepy/numbered_object_collection.py
index 1d8a087e..a157ac41 100644
--- a/montepy/numbered_object_collection.py
+++ b/montepy/numbered_object_collection.py
@@ -178,7 +178,7 @@ def __init__(
                         )
                     )
                 self.__num_cache[obj.number] = obj
-                obj._collection_ref = weakref.ref(self)
+                self._link_to_collection(obj)
             self._objects = objects
 
     def link_to_problem(self, problem):
@@ -197,18 +197,13 @@ def link_to_problem(self, problem):
             self._problem_ref = None
         else:
             self._problem_ref = weakref.ref(problem)
-        # Rebuild the number cache to ensure it reflects current object numbers
-        # after deepcopy/unpickling when the cache might be stale
-        self.__num_cache.clear()
-        for obj in self._objects:
-            self.__num_cache[obj.number] = obj
         for obj in self:
             obj.link_to_problem(problem)
             # the _collection_ref that points to the main cells collection.
             if problem is not None:
                 existing_coll = obj._collection
                 if existing_coll is None or existing_coll._problem is not problem:
-                    obj._collection_ref = weakref.ref(self)
+                    self._link_to_collection(obj)
 
     @property
     def _problem(self):
@@ -216,6 +211,26 @@ def _problem(self):
             return self._problem_ref()
         return None
 
+    def _link_to_collection(self, obj):
+        """Links the given object to this collection via a weakref.
+
+        Parameters
+        ----------
+        obj : Numbered_MCNP_Object
+            The object to link to this collection.
+        """
+        obj._collection_ref = weakref.ref(self)
+
+    def _unlink_from_collection(self, obj):
+        """Unlinks the given object from this collection.
+
+        Parameters
+        ----------
+        obj : Numbered_MCNP_Object
+            The object to unlink from this collection.
+        """
+        obj._collection_ref = None
+
     def __getstate__(self):
         state = self.__dict__.copy()
         weakref_key = "_problem_ref"
@@ -351,15 +366,9 @@ def extend(self, other_list):
                     "The object in the list {obj} is not of type: {self._obj_class}"
                 )
             if obj.number in nums:
-                try:
-                    conflicting_obj = self[obj.number]
-                    conflict_msg = (
-                        f"adding {obj} which conflicts with {conflicting_obj}"
-                    )
-                except KeyError:
-                    conflict_msg = f"adding {obj} which conflicts with existing object number {obj.number}"
                 raise NumberConflictError(
-                    f"When adding to {type(self).__name__} there was a number collision due to {conflict_msg}"
+                    f"When adding to {type(self).__name__} there was a number collision due to "
+                    f"adding {obj} which conflicts with existing object number {obj.number}"
                 )
             nums.add(obj.number)
         for obj in other_list:
@@ -511,7 +520,7 @@ def __internal_append(self, obj, **kwargs):
                 )
         self.__num_cache[obj.number] = obj
         self._objects.append(obj)
-        obj._collection_ref = weakref.ref(self)
+        self._link_to_collection(obj)
         self._append_hook(obj, **kwargs)
         if self._problem:
             obj.link_to_problem(self._problem)
@@ -523,7 +532,7 @@ def __internal_delete(self, obj, **kwargs):
         """
         self.__num_cache.pop(obj.number, None)
         self._objects.remove(obj)
-        obj._collection_ref = None
+        self._unlink_from_collection(obj)
         self._delete_hook(obj, **kwargs)
 
     def add(self, obj: Numbered_MCNP_Object):
@@ -630,7 +639,7 @@ def append_renumber(self, obj, step=1):
         number = obj.number if obj.number > 0 else 1
         if self._problem:
             obj.link_to_problem(self._problem)
-        obj._collection_ref = None
+        self._unlink_from_collection(obj)
         try:
             self.append(obj)
         except (NumberConflictError, ValueError) as e:
diff --git a/montepy/surfaces/half_space.py b/montepy/surfaces/half_space.py
index ee63dcaa..9717b7eb 100644
--- a/montepy/surfaces/half_space.py
+++ b/montepy/surfaces/half_space.py
@@ -187,22 +187,6 @@ def update_pointers(self, cells, surfaces, cell):
         if self.right is not None:
             self.right.update_pointers(cells, surfaces, cell)
 
-    def _set_cell(self, cell):
-        """Sets the _cell reference for this HalfSpace and all children.
-
-        This is used during cloning to update the _cell references to point
-        to the cloned cell rather than the original (or a deepcopied intermediate).
-
-        Parameters
-        ----------
-        cell : Cell
-            the cell this HalfSpace should be tied to.
-        """
-        self._cell = cell
-        self.left._set_cell(cell)
-        if self.right is not None:
-            self.right._set_cell(cell)
-
     def _add_new_children_to_cell(self, other):
         """Adds the cells and surfaces from a new tree to this parent cell.
 
@@ -692,19 +676,6 @@ def update_pointers(self, cells, surfaces, cell):
                     "Cell", self._cell.number, "Surface", self._divider
                 )
 
-    def _set_cell(self, cell):
-        """Sets the _cell reference for this UnitHalfSpace.
-
-        This is used during cloning to update the _cell references to point
-        to the cloned cell rather than the original (or a deepcopied intermediate).
-
-        Parameters
-        ----------
-        cell : Cell
-            the cell this UnitHalfSpace should be tied to.
-        """
-        self._cell = cell
-
     def _ensure_has_nodes(self):
         if self.node is None:
             if isinstance(self.divider, Integral):

From de5c480a0482428c208dfaecdc14840983811bd1 Mon Sep 17 00:00:00 2001
From: Micah Gale <mgale@fastmail.com>
Date: Mon, 5 Jan 2026 16:29:19 -0600
Subject: [PATCH 3/5] Update changelog.rst with release staging.

---
 doc/source/changelog.rst | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index 47e5ab58..a5f3ab2c 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -5,6 +5,13 @@ MontePy Changelog
 1.2 releases
 ============
 
+#Next Version#
+--------------
+
+**Performance Improvement**
+
+* Implement _collection_ref to link objects to their NumberedObjectCollection parent (:issue:`867`).
+
 1.2.0
 --------------
 
@@ -14,7 +21,6 @@ MontePy Changelog
 
 **Features Added**
 
-* Implement _collection_ref to link objects to their NumberedObjectCollection parent (:issue:`867`).
 * Added checking for additional input after the ``data`` block, and raising a warning if it exists (:issue:`525`).
 * Allow multiple universe fills to accept 2D MNCP lattices (:issue:`719`).
 * Make ``LatticeType.RECTANGULAR`` and ``LatticeType.HEXAHEDRAL`` synonymous (:issue:`808`).

From 7fbe1b789ff59a1d381e82b156a9823a25bb3fdb Mon Sep 17 00:00:00 2001
From: DIGVIJAY <144053736+digvijay-y@users.noreply.github.com>
Date: Fri, 9 Jan 2026 14:49:26 +0000
Subject: [PATCH 4/5] post-review

---
 demo/1_PinCellCorrection_inter.ipynb   | 12 +++++--
 demo/answers/1_PinCellCorrection.ipynb | 18 ++++++++---
 doc/source/changelog.rst               |  7 ++++
 montepy/numbered_mcnp_object.py        | 45 +++++++++++---------------
 montepy/numbered_object_collection.py  |  4 +--
 5 files changed, 51 insertions(+), 35 deletions(-)

diff --git a/demo/1_PinCellCorrection_inter.ipynb b/demo/1_PinCellCorrection_inter.ipynb
index 2909c97a..7577050c 100644
--- a/demo/1_PinCellCorrection_inter.ipynb
+++ b/demo/1_PinCellCorrection_inter.ipynb
@@ -235,7 +235,9 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.MCNP_Problem.html#montepy.MCNP_Problem\")"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.MCNP_Problem.html#montepy.MCNP_Problem\"\n",
+    ")"
    ]
   },
   {
@@ -305,7 +307,9 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.Surfaces.html#montepy.Surfaces\")"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.Surfaces.html#montepy.Surfaces\"\n",
+    ")"
    ]
   },
   {
@@ -375,7 +379,9 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.Surface.html#montepy.Surface\")"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.Surface.html#montepy.Surface\"\n",
+    ")"
    ]
   },
   {
diff --git a/demo/answers/1_PinCellCorrection.ipynb b/demo/answers/1_PinCellCorrection.ipynb
index 7485e91b..6d6a6274 100644
--- a/demo/answers/1_PinCellCorrection.ipynb
+++ b/demo/answers/1_PinCellCorrection.ipynb
@@ -234,7 +234,11 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.MCNP_Problem.html#montepy.MCNP_Problem\", 800, 600)"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.MCNP_Problem.html#montepy.MCNP_Problem\",\n",
+    "    800,\n",
+    "    600,\n",
+    ")"
    ]
   },
   {
@@ -318,7 +322,9 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.Surfaces.html#montepy.Surfaces\")"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.Surfaces.html#montepy.Surfaces\"\n",
+    ")"
    ]
   },
   {
@@ -403,7 +409,9 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.Surface.html#montepy.Surface\")"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.Surface.html#montepy.Surface\"\n",
+    ")"
    ]
   },
   {
@@ -1562,7 +1570,9 @@
    },
    "outputs": [],
    "source": [
-    "IFrame(\"https://www.montepy.org/en/stable/api/generated/montepy.MCNP_Problem.html#montepy.MCNP_Problem\")"
+    "IFrame(\n",
+    "    \"https://www.montepy.org/en/stable/api/generated/montepy.MCNP_Problem.html#montepy.MCNP_Problem\"\n",
+    ")"
    ]
   },
   {
diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index a5f3ab2c..cb686aff 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -2,6 +2,13 @@
 MontePy Changelog
 *****************
 
+unreleased
+============
+
+**Features Added**
+
+* Implement _collection_ref to link objects to their NumberedObjectCollection parent (:issue:`867`).
+
 1.2 releases
 ============
 
diff --git a/montepy/numbered_mcnp_object.py b/montepy/numbered_mcnp_object.py
index 94028fad..c4c6759f 100644
--- a/montepy/numbered_mcnp_object.py
+++ b/montepy/numbered_mcnp_object.py
@@ -16,29 +16,9 @@ def _number_validator(self, number):
     if number < 0:
         raise ValueError("number must be >= 0")
 
-    # Only validate against collection if linked to a problem
-    if self._problem is not None:
-        if self._collection is not None:
-            collection = self._collection
-        else:
-            # Find collection via _problem
-            obj_map = montepy.MCNP_Problem._NUMBERED_OBJ_MAP
-            collection_type = obj_map.get(type(self))
-
-            if collection_type is None:
-                # Finding via inheritance
-                for obj_class in obj_map:
-                    if isinstance(self, obj_class):
-                        collection_type = obj_map[obj_class]
-                        break
-
-            if collection_type is not None:
-                collection = getattr(self._problem, collection_type.__name__.lower())
-            else:
-                raise TypeError(
-                    f"Could not find collection type for {type(self).__name__} in problem."
-                )
-
+    # Only validate against collection if linked to a collection
+    if self._collection is not None:
+        collection = self._collection
         collection.check_number(number)
         collection._update_number(self.number, number, self)
 
@@ -69,8 +49,8 @@ def __init__(
         if not input:
             self._number = self._generate_default_node(int, -1)
         super().__init__(input, parser)
-        self._load_init_num(number)
         self._collection_ref = None
+        self._load_init_num(number)
 
     def _load_init_num(self, number):
         if number is not None:
@@ -142,11 +122,24 @@ def _collection(self):
             return self._collection_ref()
         return None
 
+    def _link_to_collection(self, collection):
+        """Links this object to the given collection via a weakref.
+
+        Parameters
+        ----------
+        collection : NumberedObjectCollection
+            The collection to link this object to.
+        """
+        self._collection_ref = weakref.ref(collection)
+
+    def _unlink_from_collection(self):
+        """Unlinks this object from its collection."""
+        self._collection_ref = None
+
     def __getstate__(self):
         state = super().__getstate__()
         # Remove _collection_ref weakref as it can't be pickled
-        if "_collection_ref" in state:
-            del state["_collection_ref"]
+        state.pop("_collection_ref", None)
         return state
 
     def __setstate__(self, crunchy_data):
diff --git a/montepy/numbered_object_collection.py b/montepy/numbered_object_collection.py
index a157ac41..24036c8a 100644
--- a/montepy/numbered_object_collection.py
+++ b/montepy/numbered_object_collection.py
@@ -219,7 +219,7 @@ def _link_to_collection(self, obj):
         obj : Numbered_MCNP_Object
             The object to link to this collection.
         """
-        obj._collection_ref = weakref.ref(self)
+        obj._link_to_collection(self)
 
     def _unlink_from_collection(self, obj):
         """Unlinks the given object from this collection.
@@ -229,7 +229,7 @@ def _unlink_from_collection(self, obj):
         obj : Numbered_MCNP_Object
             The object to unlink from this collection.
         """
-        obj._collection_ref = None
+        obj._unlink_from_collection()
 
     def __getstate__(self):
         state = self.__dict__.copy()

From c202b8bb6df7fdc865773b7dc2983e63e3f8981c Mon Sep 17 00:00:00 2001
From: DIGVIJAY <144053736+digvijay-y@users.noreply.github.com>
Date: Fri, 9 Jan 2026 14:57:54 +0000
Subject: [PATCH 5/5] update

---
 doc/source/changelog.rst | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index cb686aff..a5f3ab2c 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -2,13 +2,6 @@
 MontePy Changelog
 *****************
 
-unreleased
-============
-
-**Features Added**
-
-* Implement _collection_ref to link objects to their NumberedObjectCollection parent (:issue:`867`).
-
 1.2 releases
 ============