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Inter-process communication for KLayout (lyipc)

KLayout is a layout editor and viewer. It is arguably the highest-performing and most advanced layout viewer in the 100€/$ – 104€/$ range. KLayout is free software. Among its editing functions is a generic scripting interface (GSI) that supports Python and Ruby, and there are other python scripting projects that specialize in various other ways (e.g. phidl, gdspy, nazca, MatlabGDSPhotonics, KiCad, etc.).

Approaches for integrated circuit layout fall into two main categories: GUI-driven, interactive design aided by software macros; and script-driven, non-interactive programming. The latter is more repeatable, modifiable, and reusable once the script (and its library modules) has been written. The problem lies in developing the code – the layout object state and its evolution through time is realtively opaque to the programmer.

The main application of lyipc is a graphical debugging workflow that uses the excellent KLayout viewer but is not necessarily dependent on the klayout scripting language or IDE. The idea is to create a communication link between two processes:

  1. A server that is launched from within the GUI
  2. A client that can control various aspects of that GUI

By separating the processes, the server GUI can be fully featured, initializing a large virtual program memory, while the client can be pretty lightweight.

Detail: a debug process flow looks like this

  1. [process #1] Launch
    • From menu item, start a simple server on port 11078
  2. [process #2: programmer] Run a python program in either klayout or python
    • Import lyipc client package
    • Stop this program in a debugger like PDB or Spyder (examine/change program variables)
    • Write to a file "x.gds"
    • Call ipc.load("x.gds")
  3. [process #2: lyipc] The lyipc.client module will
    • Initiate a socket connection on port 11078
    • Send a command that means load
  4. [process #1] Upon receiving a connection request
    • Received command is parsed
    • An action is taken. In this case, load that file into the current view
  5. [process #2: lyipc] closes the socket and continues execution

Other uses

  • Animation: timed sequence of layouts
  • Tracing: refresh display at every step of the program
  • (future) Behavioral unit tests: Test whether code changes break previous layout behavior by keeping a reference.gds and creating a test.gds, then send them to klayout's visual diff tool.


From PyPI (Recommended)

As of version 0.1.5, installing the python package triggers a script to also install in klayout's system. All you need to do is

pip install lyipc

From github (Recommended for developers)

First, clone the project in a directory of your choice

git clone

Install the package with regular pip

pip install klayout-ipc/klayout_dot_config/python

For development mode, use pip's -e flag.

As of version 0.1.5, this will also install it into klayout, so you're done.

From klayout salt package manager

In, go to "Tools>Manage Packages". Go to "Install New Packages" and find "klayout_ipc". Double-click it, and press "Apply".

You still have to install the client module in your external-to-klayout system python The lyipc package is visible within klayout's interpreter namespace, but it is not on the system PYTHONPATH. In order for any python-based client to use it, lyipc must be installed with

pip install ~/.klayout/salt/klayout_ipc/python

or, on Windows

pip install %HOMEDRIVE%%HOMEPATH%/KLayout/salt/klayout_ipc/python

because... Windows.

Application setup

When an open file changes on disk, by default, KLayout asks whether to reload it. These prompts persist when reload is triggered by a communicating process instead of a human. Disable checks by going to's preferences > Application > General, and uncheck the box for "Check for file updates."


Server side

-- press Ctrl+I --

or go to "Tools>Inter-process communication server"

Warning: clients have the ability to close and reload layout views that are unsaved, including ones in other tabs. It is highly recommended that you start a second instance of dedicated to serving. This has to be done from command line. Tip for UNIX folks, put a shortcut to the klayout executable on your PATH

ln -s /Applications/ /usr/local/bin/klayout

Note: as of now, the port is hard-coded (11078), so there can only be one server at a time. Communication is initiated by the client as a command or query. That means using multiple clients concurrently is possible, but they would clash unless synchronized somehow.

Client side

To load a layout file in the remote window, put these lines

import lyipc.client as ipc

in a file called

Run it with either a standard python interpreter


or the klayout general scripting interface (GSI) in non-GUI mode

klayout -b -r

The former is faster because a new klayout instance is not created, but of course, the latter must be used for pya to work.

Usage examples for klayout and non-klayout layout clients are included in this repo in the "examples" folder.

Author: Alex Tait, June 2018

National Institute of Standards and Technology, Boulder, CO, USA