feat: Add timestamp argument to STEP export

Allow passing a timestamp value when export STEP files, to generate STEP
files with a specific timestamp value in the file header.

For example, a null timestamp (`0000-00-00T00:00:00`), or a static
timestamp can be used when generated files should be equal if there are
no visual changes, such as for file versioning.

This commit extends the `#export_step` function, to accept a `timestamp`
keyword argument, that can be a string or a `datetime` object. A
`datetime` is easier to use from Python.

src/build123d/exporters3d.py

@@ -29,10 +29,10 @@ license:
 # pylint has trouble with the OCP imports
 # pylint: disable=no-name-in-module, import-error
 
-from io import BytesIO
+from datetime import datetime
 import warnings
+from io import BytesIO
 from os import PathLike, fsdecode, fspath
-from typing import Union
 
 import OCP.TopAbs as ta
 from anytree import PreOrderIter
@@ -47,7 +47,11 @@ from OCP.RWGltf import RWGltf_CafWriter
 from OCP.STEPCAFControl import STEPCAFControl_Controller, STEPCAFControl_Writer
 from OCP.STEPControl import STEPControl_Controller, STEPControl_StepModelType
 from OCP.StlAPI import StlAPI_Writer
-from OCP.TCollection import TCollection_AsciiString, TCollection_ExtendedString, TCollection_HAsciiString
+from OCP.TCollection import (
+    TCollection_AsciiString,
+    TCollection_ExtendedString,
+    TCollection_HAsciiString,
+)
 from OCP.TColStd import TColStd_IndexedDataMapOfStringString
 from OCP.TDataStd import TDataStd_Name
 from OCP.TDF import TDF_Label
@@ -262,6 +266,8 @@ def export_step(
     unit: Unit = Unit.MM,
     write_pcurves: bool = True,
     precision_mode: PrecisionMode = PrecisionMode.AVERAGE,
+    *,  # Too many positional arguments
+    timestamp: str | datetime | None = None,
 ) -> bool:
     """export_step
 
@@ -302,6 +308,11 @@ def export_step(
     header = APIHeaderSection_MakeHeader(writer.Writer().Model())
     if to_export.label:
         header.SetName(TCollection_HAsciiString(to_export.label))
+    if timestamp is not None:
+        if isinstance(timestamp, datetime):
+            header.SetTimeStamp(TCollection_HAsciiString(timestamp.isoformat()))
+        else:
+            header.SetTimeStamp(TCollection_HAsciiString(timestamp))
     # consider using e.g. the non *Value versions instead
     # header.SetAuthorValue(1, TCollection_HAsciiString("Volker"));
     # header.SetOrganizationValue(1, TCollection_HAsciiString("myCompanyName"));

tests/test_exporters3d.py

@@ -30,8 +30,10 @@ import json
 import os
 import re
 import unittest
-from typing import Optional
+from datetime import datetime
 from pathlib import Path
+from typing import Optional
+from zoneinfo import ZoneInfo
 
 import pytest
 
@@ -39,7 +41,7 @@ from build123d.build_common import GridLocations
 from build123d.build_enums import Unit
 from build123d.build_line import BuildLine
 from build123d.build_sketch import BuildSketch
-from build123d.exporters3d import export_gltf, export_step, export_brep, export_stl
+from build123d.exporters3d import export_brep, export_gltf, export_step, export_stl
 from build123d.geometry import Color, Pos, Vector, VectorLike
 from build123d.objects_curve import Line
 from build123d.objects_part import Box, Sphere
@@ -144,6 +146,29 @@ class TestExportStep(DirectApiTestCase):
         os.chmod("box_read_only.step", 0o777)  # Make the file read/write
         os.remove("box_read_only.step")
 
+    def test_export_step_timestamp_datetime(self):
+        b = Box(1, 1, 1)
+        t = datetime(2025, 5, 6, 21, 30, 25)
+        self.assertTrue(export_step(b, "box.step", timestamp=t))
+        with open("box.step", "r") as file:
+            step_data = file.read()
+        os.remove("box.step")
+        self.assertEqual(
+            re.findall("FILE_NAME\\('[^']*','([^']*)'", step_data),
+            ["2025-05-06T21:30:25"],
+        )
+
+    def test_export_step_timestamp_str(self):
+        b = Box(1, 1, 1)
+        self.assertTrue(export_step(b, "box.step", timestamp="0000-00-00T00:00:00"))
+        with open("box.step", "r") as file:
+            step_data = file.read()
+        os.remove("box.step")
+        self.assertEqual(
+            re.findall("FILE_NAME\\('[^']*','([^']*)'", step_data),
+            ["0000-00-00T00:00:00"],
+        )
+
 
 class TestExportGltf(DirectApiTestCase):
     def test_export_gltf(self):