python tkinter package tk.call eval

Question

I'm using python tkinter to run tcl in python And there are two ways to run a tcl command:

import tkinter 
root = tkinter.Tk()
root.eval("winfo exists .l0")
root.tk.call("winfo exists .l0")

They have the same meaning

But what's different? And if I haven't define a widget names .l0 and can I directly use

child = ".l0"
child.winfo_exists()

? Because python told me "str has no attribute winfo_exists"

Bryan Oakley · Accepted Answer · 2017-11-15 19:40:37Z

1

The difference is that call passes each argument to tcl as a separate word, where eval will evaluate a string by first parsing it and then executing it.

In other words, this:

root.eval("winfo exists .l0")

... is functionally identical to this:

root.tk.call("winfo", "exists", ".l0")

As for the error message 'str' object has no attribute 'winfo_exists', it means exactly that. "l0" is the name of an object in the embedded tcl interpreter, but in python "l0" is just a string and python strings don't have the attribute winfo_exists.

answered Nov 15, 2017 at 19:40

Bryan Oakley

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4 Comments

shuji Over a year ago

if I need to test a window named .l0 without type of it, do you know how to deal with that?

Bryan Oakley Over a year ago

@shuji: I don't understand your question. ".l0" doesn't have a type in the world of tcl. In tcl, everything is a string. I'm sure that what you want can be done, but I can't understand what you want.

shuji Over a year ago

what I mean is that, in wish(tcl shell), I can type "winfo exists .l0" but how can I do that in python? With .l0 an unknown widget(not a topleve, frame etc.)

Bryan Oakley Over a year ago

@shuji: Like my answer shows, you can call root.tk.call and pass in whatever window name you want. That will only tell you if there is a tcl/tk window by that name, it won't tell you if a tkinter object representing that widget exists. This is a highly unusual thing to do, since with tkinter you almost never know the internal window name.

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