The Tcl interface

The Tcl class is a bridge between Python and Tcl. It can be used to initialize the interpreter, to run the mainloop, to load dll files to Tk, and to call Tcl commands from Python.

from tukaan._tcl import Tcl

Calling Tcl from Python

There are two methods to call Tcl code in Tukaan.

The first is the Tcl.call method. You can pass in arbitary number of argument of any type (see Tcl.to below), and it will evaluate it. The first argument is always the return type of the call, if you don’t expect any return it should be None

>>> Tcl.call(None, "grid", textbox_widget, *Tcl.to_tcl_args(column=3, rowspan=8))
None
>>> Tcl.call(str, textbox_widget, "get")
foobar

There’s a utility method called to_tcl_args, which can be used to convert Python keyword arguments to Tcl keyword arguments (column=3 -> ("-column", "3")). It returns a tuple, which you have to unpack, when passing into Tcl.call (with the * syntax)

The second is the Tcl.eval method, which is very similar to Python’s exec function, except in Tcl. It doesn’t do any Py-to-Tcl conversion, so you can only pass in a single string, but this means that this function is also a lot faster. Similarly to Tcl.call the first argument defines the return type. The second argument is the script to evaluate.

>>> Tcl.eval(None, "grid .app.textbox_1 -column 3 -rowspan 8")
None
>>> Tcl.eval(str, ".app.textbox_1 get")
foobar

About converting things to Tcl

You might know, that in Tcl everything is a string. Therefore Tukaan needs to convert every Python object to a string, and the strings returned from Tcl back to Python objects (this is the return value I was babbling about above). However, it isn’t simply done by calling the str() function, but finding a way, that it can be represented in Tcl. For example when a Python funciont is passed in, it creates a new Tcl procedure at C-level, which will call the Python function (if you’re really interested in this part, it’s here in _tkinter.c). An object can also be converted to Tcl, if it has a _name attribute. Widgets use this attribute to store thier pathName, with which they are represented in Tk (e.g. .frame.notebook.tab_1.button). If an object has a __to_tcl__ method, but no _name, Tcl.to will call it to represent the object to Tcl. This method is useful if you want to give a name to the object on the fly. For example, Tukaan adds a __to_tcl__ method to PIL images, which converts them to Tk images and then returns the image name, because by default PIL images aren’t known by the Tcl interpreter.

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TODO: Revise this, as it’s just a quick sketch