---
The blendfile module within BAT supports reading data from structs, such
as the Count property on an array modifier. However, blendfile only
supports modifying structs with type "char". This patch adds support for
writing structs of more types in blendfile blocks. Now, writing is
supported for ushort, short, uint, int, float, and ulong types.
The use case that inspired this patch was an instance where a file had
several array modifiers that prevented the file from being opened in
Blender on machines without large amounts of RAM. A solution using the
blendfile module may look like:
```
from blender_asset_tracer import blendfile
from pathlib import Path
b = blendfile.open_cached(Path('flag.blend'), mode='rb+')
for block in b.blocks:
if 'ArrayModifierData' in block.__str__():
try:
print('previous:', block.get(b'count'))
block.set(b'count', 1)
print('current:', block.get(b'count'))
except KeyError:
continue
b.close()
```
This would fail with the exception
`blender_asset_tracer.blendfile.exceptions.NoWriterImplemented: Setting
type Struct(b'int') is not supported for ArrayModifierData.count`. With
this patch, the above code succeeds and the count struct can be set to
a lower number that allows the file to be opened.
This solution implements missing functionality without adding any new
interfaces. A few details are:
* When deciding what type to write to the struct, the value is inferred
from what is given by the caller. If the caller gives a Python int, the
exact type is inferred from the DNA type ID. If they give a float, a
float is written. Otherwise, the existing logic is used to determine
whether to write a string or byte sequence.
* A \_write method was added to dna\_io.py that takes a Python struct
object and a value to write a byte sequence to the file object. This
method is used by public methods appropriately named to indicate what
type they will write.
* The check for whether the caller is trying to write an unsupported
type is left in place, but it has been changed to include types which
are now supported.
* Tests have been added that provide a mock file object, call the new
methods, and confirm that the correct bytes were written.
Reviewed By: sybren
Differential Revision: https://developer.blender.org/D14374
This does introduce some not-so-nice things, like having to annotate each
`__init__` function with `-> None`. However, the benefits of having static
type checking in a complex bit of software like BAT outweigh the downsides.
