Added BlendFileBlock.id_name property

Evaluated only once, so safe to call multiple times without producing
excessive disk I/O. Returns None instead of raising KeyError when there is
no (b'id', b'name') field.

blender_asset_tracer/blendfile/__init__.py

@@ -326,6 +326,7 @@ class BlendFileBlock:
         Points to the data after the block header.
         """
         self.endian = bfile.header.endian
+        self._id_name = ...  # see the id_name property
 
         header_struct = bfile.block_header_struct
         data = bfile.fileobj.read(header_struct.size)
@@ -382,6 +383,20 @@ class BlendFileBlock:
     def dna_type_name(self) -> str:
         return self.dna_type.dna_type_id.decode('ascii')
 
+    @property
+    def id_name(self) -> typing.Optional[bytes]:
+        """Same as block[b'id', b'name']; None if there is no such field.
+
+        Evaluated only once, so safe to call multiple times without producing
+        excessive disk I/O.
+        """
+        if self._id_name is ...:
+            try:
+                self._id_name = self[b'id', b'name']
+            except KeyError:
+                self._id_name = None
+        return self._id_name
+
     def refine_type_from_index(self, sdna_index: int):
         """Change the DNA Struct associated with this block.
 
@@ -543,7 +558,8 @@ class BlendFileBlock:
             -> typing.Iterator['BlendFileBlock']:
         """Dereference pointers from an array-of-pointers field.
 
-        Use this function when you have a field like materials: `Mat **mat`
+        Use this function when you have a field like Mesh materials:
+        `Mat **mat`
 
         :param path: The array-of-pointers field.
         :param array_size: Number of items in the array. If None, the
@@ -571,7 +587,8 @@ class BlendFileBlock:
             -> typing.Iterator['BlendFileBlock']:
         """Yield blocks from a fixed-size array field.
 
-        Use this function when you have a field like lamp textures: `MTex *mtex[18]`
+        Use this function when you have a field like lamp textures:
+        `MTex *mtex[18]`
 
         The size of the array is determined automatically by the size in bytes
         of the field divided by the pointer size of the blend file.

blender_asset_tracer/tracer/blocks2assets.py

@@ -5,7 +5,6 @@ From a Blend file data block, iter_assts() yields all the referred-to assets.
 
 import functools
 import logging
-import sys
 import typing
 
 from blender_asset_tracer import blendfile, bpathlib
@@ -117,10 +116,9 @@ def movie_clip(block: blendfile.BlendFileBlock) -> typing.Iterator[result.BlockU
 def object_block(block: blendfile.BlendFileBlock) -> typing.Iterator[result.BlockUsage]:
     """Object data blocks."""
     # 'ob->modifiers[...].filepath'
-    ob_idname = block[b'id', b'name']
     mods = block.get_pointer((b'modifiers', b'first'))
     for mod_idx, block_mod in enumerate(iterators.listbase(mods, next_path=(b'modifier', b'next'))):
-        block_name = b'%s.modifiers[%d]' % (ob_idname, mod_idx)
+        block_name = b'%s.modifiers[%d]' % (block.id_name, mod_idx)
         mod_type = block_mod[b'modifier', b'type']
         log.debug('Tracing modifier %s, type=%d', block_name.decode(), mod_type)