9. Troubleshooting

Where to look first

Log file: %LOCALAPPDATA%\SwPy\logs\swpy.log - add-in start, Python start, errors from the editor and the add-in. Launcher messages go to launcher.log in the same folder.
Output panel: script errors show the full traceback of your code.

The SwPy pane does not appear

Cause	Fix
SOLIDWORKS was started normally, not via the SOLIDWORKS + SwPy shortcut	Use the shortcut, or install with `install.ps1 -Machine` (admin) so SOLIDWORKS loads SwPy itself
The add-in is not registered (moved folder, other Windows user)	Run `tools\install.ps1` again from the SwPy folder
SOLIDWORKS runs as administrator	Per-user registration is invisible to elevated processes: start SOLIDWORKS normally
A message box “SwPy could not be loaded”	Read the message and `swpy.log`; usually a missing or blocked file in the SwPy folder

“Python failed to start”

SwPy looks for Python in this order: the SWPY_PYTHON_HOME environment variable, the bundled python-runtime folder next to the add-in, then installed Python versions (3.12 preferred). Check swpy.log for the path it tried. A failed start is remembered until SOLIDWORKS restarts.

A script “does nothing”

Many API methods fail silently: they return None, False or an error code instead of raising.

FeatureExtrusion2(...) returns None when nothing (or the wrong thing) is selected. Closing a sketch with InsertSketch(True) can leave nothing selected - select the sketch explicitly before creating the feature: doc.FeatureByPositionReverse(0).Select2(False, 0).
SelectByID2("Front Plane", ...) returns False when the plane has another name - company templates often rename them (XY PLANE). Use model.planes.front / .top / .right instead.

Check results and raise your own error:

feat = doc.FeatureManager.FeatureExtrusion2(...)
if feat is None:
    raise RuntimeError("extrusion failed")

Common errors

Error	Meaning / fix
`AttributeError: IModelDocExtension has no attribute 'CustomPropertyManager'. Did you mean: 'get_CustomPropertyManager'?`	An indexed property: call `get_CustomPropertyManager("")` (details)
`AttributeError: 'NoneType' object has no attribute ...`	An API call returned `None` (no active document, nothing selected, wrong name). Check the value before using it
`KeyError: 'D1@Sketch1'` from `model.dims[...]`	No dimension with that name - print `model.dims.names()`
`TypeError: No method matches given arguments`	Wrong number or type of arguments. Check the signature help (type `(`), and pass `None` for unused object parameters
`NameError: name 'doc' ...` / `doc` is `None`	No document is open (or the active window is not a document)
`RuntimeError: pip install failed`	See the pip output in the message: no internet, a typo in the package name, or no wheel for Python 3.12 x64

Other API libraries

<COM object> with no members: the object belongs to an API library that is not installed, or to an interface no library declares. Check obj.interfaces; cast explicitly if you know the interface.
The first call into Costing or Simulation takes long: SOLIDWORKS loads the add-in at that moment.
Simulation / Routing / Toolbox objects are only available when the add-in is licensed and loaded (Tools > Add-Ins).

Types and units

Values are SI: a dimension of 30 mm reads 0.03. Use to(x, mm) to display.
Mass values use the document’s material density. Templates can define a default density - if masses look 1000× off, check Mass Properties and the material in SOLIDWORKS.
Angles are radians: 45 * deg.

Never import the interop assemblies

from SolidWorks.Interop.sldworks import ... may bind to a trimmed copy embedded by another add-in and fail in confusing ways. Use sldworks.IFoo(obj) for casts and swconst for enums.

Long scripts freeze SOLIDWORKS

Scripts run on the SOLIDWORKS UI thread, so SOLIDWORKS waits until they finish. Use model.batch() around many edits and wrap long loops in ui.progress(...) - then Esc stops them. A loop without ui.progress cannot be interrupted other than by closing SOLIDWORKS - save your work before experimenting.

SOLIDWORKS only shows toolbars, menus and CommandManager tabs of add-ins registered machine-wide. Install with tools\install.ps1 -Machine (needs admin once), or use Scripts ▾ in the SwPy pane, which always works.

Reporting a problem

Include the SOLIDWORKS version (sw.RevisionNumber()), the script, the full output and the end of swpy.log.