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How to Automate AutoCAD with Python

AutoCAD exposes a COM (Component Object Model) interface on Windows that lets any language — including Python — connect to a live AutoCAD session and control it programmatically. No plugins, no special AutoCAD subscription tier, no AutoLISP required. If AutoCAD is running, Python can talk to it.

This is how the Python scripts on this site work. Here's exactly how to set it up.

What You Need

• Python 3.x — download from python.org if you don't have it
• pywin32 — the Python library that provides the Windows COM interface
• AutoCAD or Civil 3D — the full Windows desktop version (not AutoCAD web)

Install pywin32 with one command:

pip install pywin32

Connecting to a Running AutoCAD Session

Open AutoCAD and load a drawing first. Then from Python:

import win32com.client

# Connect to the running AutoCAD instance
acad = win32com.client.GetActiveObject("AutoCAD.Application")
doc = acad.ActiveDocument
msp = doc.ModelSpace

print(doc.Name)  # prints the current drawing filename

GetActiveObject finds AutoCAD already running on your machine — it doesn't launch a new instance. If AutoCAD isn't open you'll get an error, which is intentional. Always open AutoCAD and a drawing before running your script.

Sending Commands

The simplest way to control AutoCAD from Python is SendCommand — it types commands into the AutoCAD command line exactly as if you typed them yourself:

# Zoom extents
doc.SendCommand("ZOOM E\n")

# Set the current layer
doc.SendCommand("LAYER SET C-ROAD\n")

# Draw a line from 0,0 to 100,100
doc.SendCommand("LINE 0,0 100,100 \n")

The \n at the end acts as pressing Enter. This approach works for almost any AutoCAD command and is a fast way to get started.

Creating Objects via the API

For more control — and better reliability — you can create drawing objects directly through the COM API instead of sending text commands:

import win32com.client
import pythoncom

def make_point(x, y, z=0):
    pt = win32com.client.VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_R8, [x, y, z])
    return pt

acad = win32com.client.GetActiveObject("AutoCAD.Application")
msp = acad.ActiveDocument.ModelSpace

# Add a circle at 50,50 with radius 25
center = make_point(50, 50, 0)
circle = msp.AddCircle(center, 25)

# Add text
insert = make_point(10, 10, 0)
text = msp.AddText("Hello from Python", insert, 2.5)

The make_point helper is necessary because the COM API expects coordinates as a specific Windows VARIANT array type — plain Python lists won't work.

Reading Drawing Data

Python can also read data out of AutoCAD — coordinates, layer names, text content, block attributes. This is useful for generating reports or extracting data for other tools:

acad = win32com.client.GetActiveObject("AutoCAD.Application")
msp = acad.ActiveDocument.ModelSpace

for obj in msp:
    print(obj.ObjectName, obj.Layer)

This iterates every object in model space and prints its type and layer. From here you can filter by type, read coordinates, extract text values, or write data to a CSV.

Connecting to Civil 3D

Civil 3D extends the AutoCAD COM API with its own object model. You access it like this:

acad = win32com.client.GetActiveObject("AutoCAD.Application")

# Civil 3D 2025
c3d = acad.GetInterfaceObject("AeccXUiLand.AeccApplication.13.7")
c3d_doc = c3d.ActiveDocument

# Access alignments
for alignment in c3d_doc.AlignmentsSiteless:
    print(alignment.Name, alignment.Length)

The version string (13.7 for Civil 3D 2025) varies by release. You can detect it automatically or just hardcode it for your installed version.

Practical Example: Rename All Layers with a Prefix

import win32com.client

acad = win32com.client.GetActiveObject("AutoCAD.Application")
doc = acad.ActiveDocument
layers = doc.Layers

prefix = "PROJ-"
for layer in layers:
    if not layer.Name.startswith(prefix):
        layer.Name = prefix + layer.Name

print("Done — all layers renamed")

This kind of bulk operation — touching every layer in a drawing — would take minutes manually and seconds in Python. That's the real value of COM automation: anything repetitive across many objects or many drawings becomes trivial to script.

Next Steps

Once you're comfortable with the basics, the natural progression is:

• Batch processing — loop the same script across 50 DWG files
• Data extraction — pull coordinates or attributes into Excel or CSV
• Drawing generation — create standard details or title blocks programmatically
• Civil 3D automation — read alignments, feature lines, and surfaces

All of the Python scripts on this site are built on this same foundation and include the source code so you can see exactly how they work.