Add converter to voxel_size factor. (#1139)

* Add converter to voxel_size factor.

* Update changelog.

* Update converter to pass typecheck.

Author: markbader

webknossos/Changelog.md

@@ -19,6 +19,7 @@ For upgrade instructions, please check the respective _Breaking Changes_ section
 ### Changed
 
 ### Fixed
+- Add a converter to the VoxelSize field `factor`, to ensure it is a tuple.
 
 
 ## [0.14.25](https://github.com/scalableminds/webknossos-libs/releases/tag/v0.14.25) - 2024-07-18

webknossos/webknossos/dataset/dataset.py

@@ -359,7 +359,7 @@ def __init__(
             else:
                 assert (
                     self.voxel_size_with_unit == voxel_size_with_unit
-                ), f"Cannot open Dataset: The dataset {dataset_path} already exists, but the voxel_sizes do not match ({self.voxel_size} != {voxel_size})"
+                ), f"Cannot open Dataset: The dataset {dataset_path} already exists, but the voxel_sizes do not match ({self.voxel_size_with_unit} != {voxel_size_with_unit})"
             if name is not None:
                 assert (
                     self.name == name

webknossos/webknossos/dataset/properties.py

@@ -4,6 +4,7 @@
     Any,
     Callable,
     Dict,
+    Iterable,
     List,
     Optional,
     Tuple,
@@ -65,6 +66,18 @@ def _extract_num_channels(
     return array.info.num_channels
 
 
+def float_tpl(voxel_size: Union[List, Tuple]) -> Iterable:
+    # Fix for mypy bug https://github.com/python/mypy/issues/5313.
+    # Solution based on other issue for the same bug: https://github.com/python/mypy/issues/8389.
+    return tuple(
+        (
+            voxel_size[0],
+            voxel_size[1],
+            voxel_size[2],
+        )
+    )
+
+
 _properties_floating_type_to_python_type: Dict[Union[str, type], np.dtype] = {
     "float": np.dtype("float32"),
     #  np.float: np.dtype("float32"),  # np.float is an alias for float
@@ -183,7 +196,7 @@ class SegmentationLayerProperties(LayerProperties):
 
 @attr.define
 class VoxelSize:
-    factor: Tuple[float, float, float]
+    factor: Tuple[float, float, float] = attr.field(converter=float_tpl)
     unit: LengthUnit = DEFAULT_LENGTH_UNIT
 
     def to_nanometer(self) -> Tuple[float, float, float]: