Faster startup: ezdxf and vtk imported on use

.coveragerc

@@ -11,3 +11,5 @@ omit =
 exclude_lines =
     # Ignore stub body
     \.\.\.
+    # Ignore imports for type checking only
+    if TYPE_CHECKING:

cadquery/assembly.py

@@ -27,17 +27,9 @@
     UnaryConstraintKind,
     BinaryConstraintKind,
 )
-from .occ_impl.exporters.assembly import (
-    exportAssembly,
-    exportCAF,
-    exportVTKJS,
-    exportVRML,
-    exportGLTF,
-    STEPExportModeLiterals,
-)
 from .occ_impl.importers.assembly import importStep as _importStep, importXbf, importXml
 
-from .types import UnitLiterals
+from .types import UnitLiterals, STEPExportModeLiterals
 
 from .selectors import _expression_grammar as _selector_grammar
 from .utils import deprecate, BiDict, instance_of
@@ -596,6 +588,14 @@ def export(
         if mode not in get_args(STEPExportModeLiterals):
             raise ValueError(f"Unknown assembly export mode {mode} for STEP")
 
+        from .occ_impl.exporters.assembly import (
+            exportAssembly,
+            exportCAF,
+            exportVTKJS,
+            exportVRML,
+            exportGLTF,
+        )
+
         if exportType is None:
             t = path.split(".")[-1].upper()
             if t in ("STEP", "XML", "XBF", "VRML", "VTKJS", "GLTF", "GLB", "STL"):

cadquery/occ_impl/assembly.py

@@ -9,6 +9,7 @@
     Any,
     List,
     cast,
+    TYPE_CHECKING,
 )
 from typing_extensions import Protocol, Self
 from math import degrees, radians
@@ -41,19 +42,14 @@
 from OCP.TopoDS import TopoDS_Shape
 from OCP.gp import gp_EulerSequence
 
-from vtkmodules.vtkRenderingCore import (
-    vtkActor,
-    vtkPolyDataMapper as vtkMapper,
-    vtkRenderer,
-    vtkProp3D,
-)
-
 from .geom import Location
 from .shapes import Shape, Solid, Compound, GlueLiteral, _set_glue, _set_builder_options
-from .exporters.vtk import toString, extractEdgesFaces
 from ..cq import Workplane
 from ..utils import BiDict
 
+if TYPE_CHECKING:
+    from vtkmodules.vtkRenderingCore import vtkRenderer, vtkProp3D
+
 # type definitions
 AssemblyObjects = Union[Shape, Workplane, None]
 
@@ -628,7 +624,10 @@ def toVTKAssy(
     linewidth: float = 2,
     tolerance: float = 1e-3,
     angularTolerance: float = 0.1,
-) -> List[vtkProp3D]:
+) -> "List[vtkProp3D]":
+
+    from vtkmodules.vtkRenderingCore import vtkActor, vtkPolyDataMapper as vtkMapper
+    from .exporters.vtk import extractEdgesFaces
 
     rv: List[vtkProp3D] = []
 
@@ -675,7 +674,14 @@ def toVTK(
     color: Tuple[float, float, float, float] = (1.0, 1.0, 1.0, 1.0),
     tolerance: float = 1e-3,
     angularTolerance: float = 0.1,
-) -> vtkRenderer:
+) -> "vtkRenderer":
+
+    from vtkmodules.vtkRenderingCore import (
+        vtkActor,
+        vtkPolyDataMapper as vtkMapper,
+        vtkRenderer,
+    )
+    from .exporters.vtk import extractEdgesFaces
 
     renderer = vtkRenderer()
 
@@ -725,6 +731,8 @@ def toJSON(
     Export an object to a structure suitable for converting to VTK.js JSON.
     """
 
+    from .exporters.vtk import toString
+
     rv = []
 
     for shape, _, loc, col_ in assy:

cadquery/occ_impl/exporters/__init__.py

@@ -1,4 +1,5 @@
-from typing import IO, Optional, Union, cast, Dict, Any, Iterable
+from importlib import import_module
+from typing import IO, Optional, Union, cast, Dict, Any, Iterable, TYPE_CHECKING
 from typing_extensions import Literal
 
 from OCP.VrmlAPI import VrmlAPI
@@ -10,8 +11,10 @@
 from .json import JsonMesh
 from .amf import AmfWriter
 from .threemf import ThreeMFWriter
-from .dxf import exportDXF, exportDXFProjection, DxfDocument
-from .vtk import exportVTP
+
+if TYPE_CHECKING:
+    from .dxf import exportDXF, exportDXFProjection, DxfDocument
+    from .vtk import exportVTP
 
 
 class ExportTypes:
@@ -110,6 +113,8 @@ def export(
             tmfw.write3mf(f)
 
     elif exportType == ExportTypes.DXF:
+        from .dxf import exportDXF
+
         exportDXF(w, fname, **opt)
 
     elif exportType == ExportTypes.STEP:
@@ -128,6 +133,8 @@ def export(
         VrmlAPI.Write_s(shape.wrapped, fname)
 
     elif exportType == ExportTypes.VTP:
+        from .vtk import exportVTP
+
         exportVTP(shape, fname, tolerance, angularTolerance)
 
     elif exportType == ExportTypes.BREP:
@@ -138,3 +145,14 @@ def export(
 
     else:
         raise ValueError("Unknown export type")
+
+
+# lazy: importing these here would load ezdxf and vtk with cadquery
+def __getattr__(name):
+    if name in ("dxf", "vtk", "assembly"):
+        return import_module(f".{name}", __name__)
+    if name in ("exportDXF", "exportDXFProjection", "DxfDocument"):
+        return getattr(import_module(".dxf", __name__), name)
+    if name == "exportVTP":
+        return import_module(".vtk", __name__).exportVTP
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

cadquery/occ_impl/exporters/assembly.py

@@ -4,7 +4,6 @@
 from tempfile import TemporaryDirectory
 from shutil import make_archive
 from typing import Optional
-from typing_extensions import Literal
 
 from vtkmodules.vtkIOExport import vtkJSONSceneExporter, vtkVRMLExporter
 from vtkmodules.vtkRenderingCore import vtkRenderWindow
@@ -50,17 +49,14 @@
 from ..assembly import AssemblyProtocol, toCAF, toVTK, toFusedCAF
 from ..geom import Location
 from ..shapes import Shape, Compound
-from ...types import UnitLiterals
+from ...types import UnitLiterals, STEPExportModeLiterals
 
 
 class ExportModes:
     DEFAULT = "default"
     FUSED = "fused"
 
 
-STEPExportModeLiterals = Literal["default", "fused"]
-
-
 def exportAssembly(
     assy: AssemblyProtocol,
     path: str,

cadquery/occ_impl/importers/__init__.py

@@ -7,7 +7,6 @@
 
 from ... import cq
 from ..shapes import Shape
-from .dxf import _importDXF
 from ...types import UnitLiterals
 
 RAD2DEG = 360.0 / (2 * pi)
@@ -133,6 +132,8 @@ def importDXF(
     :param include: a list of layer names to import
     """
 
+    from .dxf import _importDXF
+
     faces = _importDXF(filename, tol, exclude, include)
 
     return cq.Workplane("XY").newObject(faces)

cadquery/occ_impl/shapes.py

@@ -11,6 +11,7 @@
     Self,
     TypeAlias,
     TypeVar,
+    TYPE_CHECKING,
     cast as tcast,
     overload,
     Type,
@@ -20,9 +21,6 @@
 
 from warnings import warn
 
-from vtkmodules.vtkCommonDataModel import vtkPolyData
-from vtkmodules.vtkFiltersCore import vtkTriangleFilter, vtkPolyDataNormals
-
 from OCP.ShapeBuild import ShapeBuild_ReShape
 
 from .geom import Vector, VectorLike, BoundBox, Plane, Location, Matrix
@@ -36,6 +34,9 @@
 from ..utils import multimethod, multidispatch, mypyclassmethod
 from ..types import UnitLiterals
 
+if TYPE_CHECKING:
+    from vtkmodules.vtkCommonDataModel import vtkPolyData
+
 # change default OCCT logging level
 from OCP.Message import Message, Message_Gravity
 
@@ -1711,6 +1712,9 @@ def toVtkPolyData(
         Convert shape to vtkPolyData
         """
 
+        # vtk must be loaded before getVtkPolyData(), which returns None otherwise
+        from vtkmodules.vtkFiltersCore import vtkTriangleFilter, vtkPolyDataNormals
+
         vtk_shape = IVtkOCC_Shape(self.wrapped)
         shape_data = IVtkVTK_ShapeData()
         shape_mesher = IVtkOCC_ShapeMesher()

cadquery/sketch.py

@@ -38,7 +38,6 @@
 )
 from .occ_impl.geom import Location, Vector
 from .occ_impl.exporters import export
-from .occ_impl.importers.dxf import _importDXF
 from .occ_impl.sketch_solver import (
     SketchConstraintSolver,
     ConstraintKind,
@@ -232,6 +231,8 @@ def importDXF(
         Import a DXF file and construct face(s)
         """
 
+        from .occ_impl.importers.dxf import _importDXF
+
         res = Compound.makeCompound(_importDXF(filename, tol, exclude, include))
 
         return self.face(res, angle, mode, tag)

cadquery/types.py

@@ -1,4 +1,5 @@
 from typing import Union, Literal
 
 UnitLiterals = Literal["MM", "CM", "M", "KM", "INCH", "FT", "MI", "UM", "NM"]
+STEPExportModeLiterals = Literal["default", "fused"]
 Real = Union[int, float]

tests/test_lazy_imports.py

@@ -0,0 +1,45 @@
+import os
+import subprocess
+import sys
+
+import pytest
+
+import cadquery
+from cadquery.occ_impl import exporters
+from cadquery.occ_impl.exporters import assembly, dxf, vtk
+
+
+def test_import_does_not_load_ezdxf_or_vtk():
+    # a fresh interpreter: this process has ezdxf and vtk loaded by other tests
+    code = (
+        "import sys, cadquery as cq;"
+        "print({m.split('.')[0] for m in sys.modules} & {'ezdxf', 'vtkmodules'});"
+        # the submodules stay reachable through the packages
+        "cq.exporters.assembly.ExportModes, cq.exporters.dxf, cq.exporters.vtk;"
+        "print('ok')"
+    )
+    # run next to the package under test; only stdout is checked, since the
+    # interpreter may crash on exit on Windows (#1911)
+    out = subprocess.run(
+        [sys.executable, "-u", "-c", code],
+        cwd=os.path.dirname(os.path.dirname(cadquery.__file__)),
+        capture_output=True,
+        text=True,
+    )
+
+    assert out.stdout.split() == ["set()", "ok"], out.stdout + out.stderr
+
+
+def test_exporters_lazy_names():
+    # the submodules are attributes here already, so ask __getattr__ directly
+    assert exporters.__getattr__("dxf") is dxf
+    assert exporters.__getattr__("vtk") is vtk
+    assert exporters.__getattr__("assembly") is assembly
+
+    assert exporters.exportDXF is dxf.exportDXF
+    assert exporters.exportDXFProjection is dxf.exportDXFProjection
+    assert exporters.DxfDocument is dxf.DxfDocument
+    assert exporters.exportVTP is vtk.exportVTP
+
+    with pytest.raises(AttributeError):
+        exporters.nonexistent