From 616eb277c3ead18e0003a54d029294ea6d1e382e Mon Sep 17 00:00:00 2001
From: "Hans J. Johnson" <hans-johnson@uiowa.edu>
Date: Thu, 20 Aug 2026 08:53:58 -0500
Subject: [PATCH] COMP: Resolve Python ST/IT/OT from the wrapped C types

Wrapping/WrapBasicTypes.cmake selects unsigned long long for
itk::IdentifierType only when both WIN32 and ITK_USE_64BITS_IDS hold,
while itk.support.types derived the alias independently. On Windows with
ITK_USE_64BITS_IDS=OFF the wrapping instantiates unsigned long while
itk.IT reported a 64-bit type, so itk.VectorContainer[itk.IT, ...] named
an instantiation that does not exist.

Export the mangled names ITKM_ST, ITKM_IT and ITKM_OT through itkConfig
and look the aliases up from there, so the Python aliases and the
instantiated templates come from one definition.
---
 .../Generators/Python/itk/support/types.py    | 19 +++++++++++++++----
 .../Python/itkConfig.template.in.py           |  8 ++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/Wrapping/Generators/Python/itk/support/types.py b/Wrapping/Generators/Python/itk/support/types.py
index 9eb29cfc1b9..ebed191ab66 100644
--- a/Wrapping/Generators/Python/itk/support/types.py
+++ b/Wrapping/Generators/Python/itk/support/types.py
@@ -22,6 +22,8 @@
 from typing import Self, TypeAlias, Union, TYPE_CHECKING
 import os
 
+from itkConfig import ITK_GLOBAL_WRAPPING_TYPE_ALIASES
+
 try:
     from numpy.typing import ArrayLike
 except ImportError:
@@ -157,10 +159,19 @@ def initialize_c_types_once(cls) -> tuple[Self, ...]:
 int32_t = SI
 int64_t = SL if SL.dtype.itemsize == 8 else SLL
 
-# Aliases for SizeValueType, IdentifierType, OffsetType
-ST = uint64_t
-IT = uint64_t
-OT = int64_t
+# Aliases for SizeValueType, IdentifierType, OffsetType, resolved from the
+# C types the wrapping actually instantiated rather than re-derived here.
+_c_type_by_mangled_name: dict[str, itkCType] = {
+    "UL": UL,
+    "ULL": ULL,
+    "SL": SL,
+    "SLL": SLL,
+}
+ST = _c_type_by_mangled_name[ITK_GLOBAL_WRAPPING_TYPE_ALIASES["ST"]]
+IT = _c_type_by_mangled_name[ITK_GLOBAL_WRAPPING_TYPE_ALIASES["IT"]]
+OT = _c_type_by_mangled_name[ITK_GLOBAL_WRAPPING_TYPE_ALIASES["OT"]]
+del _c_type_by_mangled_name
+del ITK_GLOBAL_WRAPPING_TYPE_ALIASES
 
 # Type aliases to avoid expensive import, circular references. Use with forward references.
 if TYPE_CHECKING:
diff --git a/Wrapping/Generators/Python/itkConfig.template.in.py b/Wrapping/Generators/Python/itkConfig.template.in.py
index b6cd5d98331..b5f20020612 100644
--- a/Wrapping/Generators/Python/itkConfig.template.in.py
+++ b/Wrapping/Generators/Python/itkConfig.template.in.py
@@ -194,6 +194,14 @@ def _normalized_path(relative_posix_path: str, message) -> str:
     "ITK_WRAP_PYTHON_COMPLEX_REAL": "@ITK_WRAP_PYTHON_COMPLEX_REAL@".split(";"),
 }
 
+# Mangled names of the C types the wrapping instantiated for itk::SizeValueType,
+# itk::IdentifierType and itk::OffsetValueType, from Wrapping/WrapBasicTypes.cmake.
+ITK_GLOBAL_WRAPPING_TYPE_ALIASES: dict[str, str] = {
+    "ST": "@ITKM_ST@",
+    "IT": "@ITKM_IT@",
+    "OT": "@ITKM_OT@",
+}
+
 (swig_lib, swig_py, config_py, doxygen_root, path) = _initialize()
 del _initialize
 del warnings