fix issues.

- fix issue according to python linter
- do not write vt group if no changes. reduce the cost of virtools group class.

bbp_ng/OP_IMPORT_virtools.py

@@ -236,7 +236,7 @@ def _import_virtools_meshes(
 
                     # return
                     yield face
-            def mtl_iterator() -> typing.Iterator[bpy.types.Material]:
+            def mtl_iterator() -> typing.Iterator[bpy.types.Material | None]:
                 for vtmtl in vtmesh.get_material_slots():
                     if vtmtl:
                         yield material_cret_map.get(vtmtl, None)

bbp_ng/PROP_ballance_element.py

@@ -36,7 +36,7 @@ class BallanceElementType(enum.IntEnum):
 
 _g_ElementCount: int = len(BallanceElementType)
 _g_ElementNameIdMap: dict[str, int] = dict((entry.name, entry.value) for entry in BallanceElementType)
-_g_ElementIdNameMap: dict[str, int] = dict((entry.value, entry.name) for entry in BallanceElementType)
+_g_ElementIdNameMap: dict[int, str] = dict((entry.value, entry.name) for entry in BallanceElementType)
 
 def get_ballance_element_id(name: str) -> int | None:
     """
@@ -47,7 +47,7 @@ def get_ballance_element_id(name: str) -> int | None:
     """
     return _g_ElementNameIdMap.get(name, None)
 
-def get_ballance_element_name(id: int) -> int | None:
+def get_ballance_element_name(id: int) -> str | None:
     """
     Get Ballance element name by its ID
 
@@ -250,10 +250,10 @@ class BallanceElementsHelper():
             return mesh
 
         # if no existing one, create new one
-        new_mesh_name: str | None = get_ballance_element_id(element_id)
+        new_mesh_name: str | None = get_ballance_element_name(element_id)
         if new_mesh_name is None: 
             raise UTIL_functions.BBPException('invalid element id')
-        new_mesh: bpy.types.Mesh = bpy.data.meshes.new(get_ballance_element_name(element_id))
+        new_mesh: bpy.types.Mesh = bpy.data.meshes.new(new_mesh_name)
 
         _load_element(new_mesh, element_id)
         self.__mElementMap[element_id] = new_mesh

bbp_ng/PROP_virtools_group.py

@@ -28,12 +28,14 @@ class VirtoolsGroupsHelper():
     """
     __mSingletonMutex: typing.ClassVar[bool] = False
     __mIsValid: bool
+    __mNoChange: bool ##< A bool indicate whether any change happended during lifetime. If no change, skip the writing when exiting.
     __mAssocObj: bpy.types.Object
     __mGroupsSet: set[str]
     
     def __init__(self, assoc: bpy.types.Object):
         self.__mGroupsSet = set()
         self.__mAssocObj = assoc
+        self.__mNoChange = True
         
         # check singleton
         if VirtoolsGroupsHelper.__mSingletonMutex:
@@ -56,8 +58,10 @@ class VirtoolsGroupsHelper():
     
     def dispose(self) -> None:
         if self.is_valid():
+            # if have changes,
             # write to ballance elements property and reset validation
-            self.__write_to_virtools_groups()
+            if not self.__mNoChange:
+                self.__write_to_virtools_groups()
             self.__mIsValid = False
             VirtoolsGroupsHelper.__mSingletonMutex = False
     
@@ -67,18 +71,22 @@ class VirtoolsGroupsHelper():
     
     def add_group(self, gname: str) -> None:
         self.__check_valid()
+        self.__mNoChange = False
         self.__mGroupsSet.add(gname)
     
     def add_groups(self, gnames: typing.Iterable[str]) -> None:
         self.__check_valid()
+        self.__mNoChange = False
         self.__mGroupsSet.update(gnames)
     
     def remove_group(self, gname: str) -> None:
         self.__check_valid()
+        self.__mNoChange = False
         self.__mGroupsSet.discard(gname)
     
     def remove_groups(self, gnames: typing.Iterable[str]) -> None:
         self.__check_valid()
+        self.__mNoChange = False
         for gname in gnames:
             self.__mGroupsSet.discard(gname)
     
@@ -103,6 +111,7 @@ class VirtoolsGroupsHelper():
     
     def clear_all_groups(self):
         self.__check_valid()
+        self.__mNoChange = False
         self.__mGroupsSet.clear()
     
     def __write_to_virtools_groups(self) -> None: