JHamidun AutoCAD over COM
Что нужно до начала
Только Windows. COM/ActiveX — механизм Windows; на macOS и Linux этот навык неприменим целиком, а не частично.
pip install pywin32 pillow
pywin32 даёт win32com, pythoncom и win32gui; pillow нужен только для
снятия скриншота окна. CAD должен быть установлен и запущен — навык
подключается к работающему приложению, а не поднимает его с нуля.
Проверить связку одной строкой, не открывая редактор:
python -c "import win32com.client as c; print(c.GetActiveObject('AutoCAD.Application').Name)"
Ошибка здесь читается по тексту — таблица в разделе «Connecting» разбирает три разных случая, которые выглядят одинаково.
Overview
Any CAD with the AutoCAD-compatible ActiveX object model is driven the same way
from Python: win32com.client talks to a running application, and the drawing
is built by calling methods on ModelSpace. Nothing is installed into the CAD,
nothing is compiled, and SECURELOAD / TRUSTEDPATHS never enter the picture
because no code is loaded inside the application.
Core principle: the COM layer lies quietly. Calls return success, variables
read back the value you set, and the drawing is still wrong. Verify geometry by
measuring it (GetBoundingBox, Volume, entity counts), never by reading back
the setting you just wrote.
When to Use
- Drawing or editing entities, layers, blocks, dimensions, hatches, 3D solids
- Building paper-space sheets and viewports
- Reading a drawing's contents or measuring what is in it
- Diagnosing why a CAD will not accept an external connection
Do not use for: AutoCAD LT — it is not an ActiveX server and cannot be reached
from another process at all. Its only automation surface is AutoLISP text plus
.scr scripts. Nothing in this skill applies to it.
Connecting
import pythoncom, win32com.client
pythoncom.CoInitialize()
app = win32com.client.GetActiveObject("AutoCAD.Application") # already running
GetActiveObject attaches to a running instance; Dispatch launches one, slowly
and with focus stealing. Prefer the former, fall back to the latter.
Read the COM error text — it distinguishes three different situations:
| Error text | Meaning |
|---|---|
Недопустимая строка с указанием класса (CO_E_CLASSSTRING) |
ProgID not registered — the program is not installed |
Операция недоступна (MK_E_UNAVAILABLE) |
Registered, but no instance running |
Ошибка при выполнении приложения-сервера (CO_E_SERVER_EXEC_FAILURE) |
Windows tried to launch it and the process died |
ProgIDs: AutoCAD.Application (also versioned, .26 = 2027), GstarCAD.Application,
ZWCAD.Application, BricscadApp.AcadApplication, nanoCAD.Application.
On the Start tab no document exists — app.ActiveDocument raises, so catch it and
call app.Documents.Add().
Points and arrays
Every point argument is a VARIANT array of doubles, never a Python list:
from win32com.client import VARIANT
def pt(x, y, z=0.0):
return VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_R8, [float(x), float(y), float(z)])
Polylines take one flat array [x1, y1, x2, y2, ...]. Object arrays (hatch
boundaries) take VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_DISPATCH, [...]).
Quick reference — the failures that cost real time
| Symptom | Cause | Fix |
|---|---|---|
| Dimension lines drawn, no text or arrows | SetVariable("DIMSCALE", n) does not reach entities created through ActiveX |
dim.ScaleFactor = n on the object, then doc.Regen(1) |
| Mass/filter by colour misses the biggest parts | Boolean resets the result to ByLayer (256) | Identify parts by volume or layer, never by colour after a Boolean |
Сервер RPC недоступен, AutoCAD gone |
Deleted every object in a layout, including its last viewport | Delete only ObjectName != "AcDbViewport"; reuse existing viewports |
Ошибка при установке текущего видового экрана |
ActivePViewport set before entering model space |
doc.MSpace = True first, then assign |
PlotToFile returns True, no file or a 2 KB stub |
BACKGROUNDPLOT defaults to 2 |
Set it to 0; prefer building the PDF outside the CAD |
Недопустимый аргумент type в ZoomScaled |
Wrong enum | 0 absolute, 1 relative, 2 relative-to-paper |
Неоднородное масштабирование невозможно |
Solids accept uniform scaling only — a sphere cannot be squashed into an ellipsoid | Build oval bodies from an elliptical profile: AddEllipse → AddRegion → AddExtrudedSolid |
Неверный ввод from AddRegion |
AddPolyline makes a 3D polyline, and a region needs a planar curve |
Draw the profile as a lightweight polyline in XY, then Rotate3D it upright |
| Drawing extents far larger than the model | AddRegion, AddExtrudedSolid and AddRevolvedSolid do not consume their input |
Delete the source curve and the region after creating the solid |
Вызов был отклонен (RPC_E_CALL_REJECTED) |
The application is busy redrawing | Retry the call after a second; it is transient, not an error in the code |
Every property suddenly fails with <unknown>.Name, <unknown>.Count |
An unterminated SendCommand left the CAD waiting at the command line, which blocks the whole ActiveX interface. It looks exactly like a corrupt pywin32 cache and is not — clearing gen_py changes nothing |
Send ESC to the window (WScript.Shell.SendKeys("{ESC}")), then set visual styles through system variables instead: VSFACESTYLE=1, VSEDGES=2. Guard with doc.GetVariable("CMDACTIVE") |
Вызванный объект был отключен от клиентов |
Read a property of a document after Close() |
Capture .Name before closing |
A newly added document has no ModelSpace |
Documents.Add() returns before the document is usable |
Retry for a few seconds |
Module list shows only ntdll + wow64* |
64-bit tooling cannot enumerate a 32-bit process | Use C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe |
| Window screenshots land ~300 px off | Display scaling above 100 % | ctypes.windll.user32.SetProcessDPIAware() before GetWindowRect |
| Screenshot grab fails, or the window "is not found" | Matched windows by title and size; a minimised frame reports a tiny rect and tooltips share the title | Match by owning process id, ShowWindow(RESTORE) then MAXIMIZE, poll until the rect is big |
| A property tooltip sits in the middle of the capture | The cursor is hovering over a solid | SetCursorPos to a corner before grabbing |
Verify by measuring
mn, mx = solid.GetBoundingBox() # returns two 3-tuples
print(mx[0] - mn[0], mx[1] - mn[1], mx[2] - mn[2])
print(solid.Volume / 1e6, "litres")
Cross-check the volume against a hand calculation before trusting a model. A shell built as outer-box minus cavity minus opening must equal the sum of its equivalent plates; if it does not, the geometry is wrong regardless of how it looks on screen.
Commands and language
SendCommand is asynchronous and returns nothing — anything that depends on its
result must wait, and a following ZoomExtents will otherwise run first. Prefix
commands with . and options with _ so they survive a localised build:
doc.SendCommand("._VSCURRENT\n_E\n").
Implementation
cookbook.py in this directory holds working helpers: connection with fallback,
point and object arrays, 3D solid construction with Booleans, cylinders on the X
and Y axes, dimension creation that is actually visible, paper-space sheets, and
window capture. Copy what is needed rather than importing it.
Отдельно стоит знать про четыре из них — они закрывают ровно те ловушки, что описаны выше, и без них таблица симптомов остаётся теорией:
| Помощник | Закрывает |
|---|---|
attach_only() |
подключиться, но не запускать CAD: пакетный прогон, чужая машина, работа по расписанию. У connect() запуск — штатное поведение |
send_command() |
асинхронность SendCommand: ждёт по CMDACTIVE, пока команда действительно завершится, и снимает зависшую через ESC |
visual_style() |
то же, что ._VSCURRENT, но системными переменными — не трогает командную строку и потому не может её подвесить |
cad_window() |
поиск окна по идентификатору процесса с разворачиванием и ожиданием настоящего размера, вместо совпадения по заголовку |
Common mistakes
- Trusting a system variable read-back.
DIMSCALEreads 50 while entities render at 2.5. Measure the entity, not the variable. - Screenshotting a shaded view on a white background. Colour 7 is white on dark and black on light; a plan on a white figure can look completely empty while every entity is present. Count entities before concluding anything.
- Assuming a colour survives editing. Only Booleans reset it, which is exactly when it matters most.
- Plotting from the CAD. The PDF drivers plot in the background and fail silently. Generating the sheet with matplotlib from the same data is faster and actually verifiable.