Allow clearing default material libraries by assigning None

doc/source/changelog.rst

@@ -8,6 +8,9 @@ MontePy Changelog
 #Next Version#
 --------------
 
+**Features Added**
+
+* Allow clearing default libraries by assigning ``None`` at material and problem scopes; unset values are omitted from serialization.
 
 **Features Added**
 

montepy/data_inputs/material.py

@@ -59,12 +59,37 @@ def __getitem__(self, key):
         except KeyError:
             return None
 
+    def update(self, other=None, **kwargs):
+        """Update the default libraries with the key/value pairs from other, overwriting existing keys.
+
+        Parameters
+        ----------
+        other : dict or dict-like
+            Another dict or dict-like object to update from
+        **kwargs
+            Additional key-value pairs to update
+        """
+        if other is not None:
+            if hasattr(other, "items"):
+                for key, value in other.items():
+                    self[key] = value
+            else:
+                for key, value in other:
+                    self[key] = value
+        for key, value in kwargs.items():
+            self[key] = value
+
     def __setitem__(self, key, value):
         key = self._validate_key(key)
+        if value is None:
+            # Setting to None means unset/delete the library
+            try:
+                del self[key]
+            except KeyError:
+                pass  # Already unset, nothing to do
+            return
         if not isinstance(value, (Library, str)):
-            raise TypeError(
-                f"Value must be a library or str. {value} of type: {type(value).__name__} given."
-            )
+            raise TypeError("Default library value must be a Library, str, or None")
         if isinstance(value, str):
             value = Library(value)
         try:
@@ -252,16 +277,22 @@ class Material(data_input.DataInputAbstract, Numbered_MCNP_Object):
     :func:`~montepy.data_inputs.material.Material.default_libraries` acts like a dictionary,
     and can accept a string or a :class:`~montepy.particle.LibraryType` as keys.
 
+    To clear a default library, assign ``None``:
+
     .. testcode::
 
         print(mat.default_libraries["plib"])
         mat.default_libraries[montepy.LibraryType.NEUTRON] = "00c"
         print(mat.default_libraries["nlib"])
+        # Clear/unset the plib default
+        mat.default_libraries["plib"] = None
+        print(mat.default_libraries["plib"])
 
     .. testoutput::
 
         80p
         00c
+        None
 
     See Also
     --------
@@ -437,16 +468,22 @@ def default_libraries(self):
         :func:`~montepy.data_inputs.material.Material.default_libraries` acts like a dictionary,
         and can accept a string or a :class:`~montepy.particle.LibraryType` as keys.
 
+        To clear a default library, assign ``None``:
+
         .. testcode::
 
             print(mat.default_libraries["plib"])
             mat.default_libraries[montepy.LibraryType.NEUTRON] = "00c"
             print(mat.default_libraries["nlib"])
+            # Clear/unset the plib default
+            mat.default_libraries["plib"] = None
+            print(mat.default_libraries["plib"])
 
         .. testoutput::
 
             None
             00c
+            None
 
         .. versionadded:: 1.0.0
 

montepy/materials.py

@@ -218,7 +218,7 @@ def default_libraries(self) -> dict[montepy.LibraryType, montepy.Library]:
         ^^^^^^^^
 
         To set the default libraries for a problem you need to set this dictionary
-        to a Library or string.
+        to a Library or string. To clear a default library, assign ``None``.
 
         .. testcode:: python
 
@@ -229,6 +229,8 @@ def default_libraries(self) -> dict[montepy.LibraryType, montepy.Library]:
             problem.materials.default_libraries["nlib"] = "00c"
             # set photo-atomic
             problem.materials.default_libraries[montepy.LibraryType.PHOTO_ATOMIC] = montepy.Library("80p")
+            # clear/unset neutron default
+            problem.materials.default_libraries["nlib"] = None
 
         .. versionadded:: 1.0.0
 

pyproject.toml

@@ -14,6 +14,7 @@ authors = [
 	{name = "Brenna Carbno", email="[email protected]"},
 	{name = "Benjaminas Marcinkevicius", email="[email protected]"},
 	{name = "Paul Ferney", email="[email protected]"},
+	{name = "Vikranth Udandarao", email="[email protected]"},
 	{name = "Digvijay Yeware", email="[email protected]"}
 ]
 keywords = ["MCNP", "neutronics", "imcnp", "input file", "monte carlo", "radiation transport"]

tests/test_material.py

@@ -877,3 +877,30 @@ def test_bad_set_get(_, dl):
 
     def test_dl_str(_, dl):
         str(dl)
+
+    def test_default_libraries_none_setting(_, dl):
+        """Test that setting default libraries to None unsets them."""
+        # Set a library first
+        dl["plib"] = "80p"
+        assert dl["plib"] == Library("80p")
+
+        # Set to None to unset
+        dl["plib"] = None
+        assert dl["plib"] is None
+
+        # Setting None on unset library should not error
+        dl["nlib"] = None
+        assert dl["nlib"] is None
+
+        # Test with enum keys
+        dl[LibraryType.PHOTO_ATOMIC] = "90p"
+        assert dl["plib"] == Library("90p")
+        dl[LibraryType.PHOTO_ATOMIC] = None
+        assert dl["plib"] is None
+
+        # Test update method with None
+        dl["nlib"] = "00c"
+        dl["plib"] = "80p"
+        dl.update({"plib": None})
+        assert dl["plib"] is None
+        assert dl["nlib"] == Library("00c")