Did you know that Python is natively compatible with Tcl?

As a matter of fact, Tk is the de-facto language used for Python GUI front-ends: for example, IDLE is entirely written using Tk calls from within Python.

The native Python module that enables Tcl integration is called tkinter:

# import the Tcl object
from tkinter import Tcl

# create a new Tcl interpreter
tcl = Tcl()

# example Tcl calls
tcl.eval('set myTclVariable {%s}' % 1)

This module effectively enables you to make Tcl calls in the current Python process, and is 100% embedded: there’s no child Tcl process; the actual Tcl interpreter is embedded within the current Python process, and the pid of both Python and Tcl is the same.


making Tcl calls within Python is in effect, passing a string (str) object to the eval attribute of Tcl instance object. Therefore string operations (such as substitution) is perfectly supported/legal.

However, the raw functionality provided by this module is rather crude. Crude in the sense that whilst it does provides the basic fundamental infrastructure, allowing users to practically make any and all calls to Tcl (including loading other packages), it does not provide an additional layer on top of the Tcl language to make it more user friendly. Example:

from tkinter import Tcl

tcl = Tcl()

# load up Tclx
tcl.eval('package require Tclx')

# create a keyed list
tcl.eval('keylset myKlist key_a value_a key_b value_b')

# wouldn't it be nice to be able to cast the tcl keyed list to a python
# object, instead of having to do this?
key_a_value = tcl.eval('keylget myKlist key_a')
key_b_value = tcl.eval('keylget myKlist key_b')

Documentation to tkinter can be found at:

Tcl Enhanced

Part of pyATS goal is to enable the testing community to leverage existing Tcl-based scripts and libraries. In order to make the integration easier, the tcl module was created to extend the native Python-Tcl interaction:

  • Interpreter class: extends the native Tcl interpreter by providing access to ATS-tree packages & libraries.

  • Two-Way Typecasting: APIs and Python classes, enabling typecasting Tcl variables to its appropriate Python objects and back. Including but not limited to: int, list, string, array, keyed lists etc.

  • Call history: maintaining a historical record of Tcl API calls for debugging purposes.

  • Callbacks: callbacks from Tcl to Python code, enabling closer coupling

  • Dictionary Access: accessing Tcl variables as if accessing a python dictionary.

  • Magic Q Calls: calling Tcl APIs as if calling a python object method, with support for Python *args and **kwargs mapping to Tcl positional and dashed arguments.


The following is required for this module to function:

  1. tkinter module compiled and working

When Python is first compiled, it looks up the current environment to determine what modules can be compiled & linked, and what is missing. This information is printed out at the end of make.

The base Python tkinter module is compiled only when Python detects the presence of Tcl header files, and can link the compiled module against Tcl *.so files. This is step automatically done if you are using the build_python script supplied with pyATS installation. You can verify whether tkinter was compiled and linked properly in Python by importing the module and trying to create an interpreter instance as shown in introduction above.