Bugfix: DES subheader load (#36)

Author: pressler-vsc

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- `jbpy.core.DataExtensionSegment.load()` for DES subheaders with conditional, user-defined fields
+
 
 ## [0.5.0] - 2025-12-16
 

jbpy/core.py

@@ -21,7 +21,7 @@
 import os
 import re
 from collections.abc import Callable, Iterable
-from typing import Any, Iterator, Literal, Self
+from typing import Any, Final, Iterator, Literal, Self
 
 logger = logging.getLogger(__name__)
 
@@ -764,7 +764,7 @@ class ComponentCollection(JbpIOComponent):
 
     def __init__(self, name: str):
         super().__init__(name)
-        self._children: list[JbpIOComponent] = []
+        self._children: Final[list[JbpIOComponent]] = []
 
     def __eq__(self, other):
         if not isinstance(other, type(self)):
@@ -774,7 +774,7 @@ def __eq__(self, other):
             [left == right for left, right in zip(self._children, other._children)]
         )
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self._children)
 
     def _contains(self, item):

jbpy/extensions/des_subheader/xml_data_content.py

@@ -134,14 +134,14 @@ def __init__(self, name):
             ),
         ]
 
-    def _populate_user_defined_subheader(self, desshl_field):
+    def _populate_user_defined_subheader(self, desshl_field) -> None:
         if desshl_field.value not in self.allowed_subheader_lengths:
             logger.warning(
                 f"Invalid user defined subheader length. {desshl_field.value} not in {self.allowed_subheader_lengths}"
             )
 
         # remove current user-defined subheader fields
-        self._children = self._children[: self._children.index(desshl_field) + 1]
+        del self._children[self._children.index(desshl_field) + 1 :]
         current_size = 0
         for field in self.all_fields:
             if current_size == desshl_field.value:

jbpy/extensions/tre/REGPTB.py

@@ -95,4 +95,4 @@ def _num_pts_handler(self, field: core.Field) -> None:
                 ),
             )
         if num < num_before:
-            self._children = self._children[: 3 + (6 * num)]
+            del self._children[3 + (6 * num) :]

test/test_jbpy.py

@@ -27,6 +27,19 @@ def test_roundtrip_jitc_quicklook(filename, tmp_path):
 
     assert ntf == ntf2
 
+    file_components_to_compare = [ntf["FileHeader"]]
+    for segtype in list(ntf.values())[1:]:
+        file_components_to_compare.extend(x["subheader"] for x in segtype)
+    for component in file_components_to_compare:
+        with filename.open("rb") as f_orig, copy_filename.open("rb") as f_copy:
+            offset = component.get_offset()
+            size = component.get_size()
+            f_orig.seek(offset)
+            bytes_orig = f_orig.read(size)
+            f_copy.seek(offset)
+            bytes_copy = f_copy.read(size)
+            assert bytes_orig == bytes_copy
+
 
 EXPECTED_TRES = (
     "BLOCKA",