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tkinter focus_get() with non-tkinter Tk widget #88758
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The purpose of focus_get() is to return the widget that currently has the focus. It tries to convert its result to a tkinter widget, which can fail, because not all Tk widgets are known to tkinter. Consider this, for example: import tkinter
def print_focused_widget():
print(repr(root.focus_get()))
root.after(1000, print_focused_widget)
root = tkinter.Tk()
menu = root["menu"] = tkinter.Menu()
menu.add_cascade(label="Click here", menu=tkinter.Menu())
print_focused_widget()
tkinter.mainloop() Output, with menu clicked after a couple seconds (on Linux): None
<tkinter.Tk object .>
<tkinter.Tk object .>
Exception in Tkinter callback
Traceback (most recent call last):
File "/home/akuli/.local/lib/python3.10/tkinter/__init__.py", line 1916, in __call__
return self.func(*args)
File "/home/akuli/.local/lib/python3.10/tkinter/__init__.py", line 838, in callit
func(*args)
File "/home/akuli/porcu/foo.py", line 4, in print_focused_widget
print(repr(root.focus_get()))
File "/home/akuli/.local/lib/python3.10/tkinter/__init__.py", line 782, in focus_get
return self._nametowidget(name)
File "/home/akuli/.local/lib/python3.10/tkinter/__init__.py", line 1531, in nametowidget
w = w.children[n]
KeyError: '#!menu' Some nametowidget() calls in tkinter/init.py already handle this correctly. Consider winfo_children(), for example:
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Forgot to mention: The correct fix IMO would be to return None when a KeyError occurs. This way code like |
I agree with Akuli that raising a KeyError is not expected behaviour (combined with the fact this is caught elsewhere), and therefore is probably a regression. While we could use Akuli, would you like to create a pull request for this? |
Sorry, I should specify that we would use |
It is a duplicate of bpo-734176. |
I found bpo-734176 before I created this. It is NOT a duplicate. While bpo-734176 is about menus, this one is about focus_get(), and not necessarily related to menus. In fact, I initially noticed this with an "open file" dialog, not with a menu. I'm not putting my address into your CLA, thank you very much. |
Akuli, what tk widgets do you think are not known to tkinter? In any case, tk menu is known to tkinter. I cannot reproduce when running on Windows with 3.10.0b3: Add "print(root.children)" (after add_cascade) results in {'!menu': <tkinter.Menu object .!menu>, '!menu2': <tkinter.Menu object .!menu2>}. The names are created in tkinter.py lines 2564-2573. I then see 'None' once and then '<tkinter.Tk object .>' indefinitely even while hovering over and clicking 'click me' and the dropdown. If I click outside the tk box, the print returns to 'None'. Maybe there is an OS difference in what is considered to have 'focus'. Key '#!menu' looks like '!menu' with '#' prepended. Someone could try changing the tkinter code referenced above and see if the change appears in the bad key. Also check the contents of root.children. |
I am not quite convinced that this is a duplicate of bpo-734176. The latter is about tearoff clones and nothing is cloned here. But I do notice that number 'names were also prefixed with '#'. What happens if 'tearoff=0' is added to the cascade so that it is not even clonable. The tkinter naming of instances after the class was added less than 10 years ago. |
Unfortunately I don't know any real-world examples of this on Windows. The open file dialog works very differently on Windows: it uses the native Windows dialog, whereas on Linux, it's implemented in Tcl. Meanwhile, here's a platform-independent toy example: import tkinter
root = tkinter.Tk()
root.tk.eval("""
entry .e
pack .e
focus .e
""")
root.after(500, root.focus_get)
root.mainloop() Also, thanks for reopening! |
Traceback (most recent call last):
File "C:\Programs\Python310\lib\tkinter\__init__.py", line 1921, in __call__
return self.func(*args)
File "C:\Programs\Python310\lib\tkinter\__init__.py", line 839, in callit
func(*args)
File "C:\Programs\Python310\lib\tkinter\__init__.py", line 783, in focus_get
return self._nametowidget(name)
File "C:\Programs\Python310\lib\tkinter\__init__.py", line 1536, in nametowidget
w = w.children[n]
KeyError: 'e' Is catching KeyError in the following Silently failing when asked to focus on something is even less obviously correct. For 'widget = root.focus_get' to assign None to widget is not obviously useful as it likely just delays the error. |
Here are the options:
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Typo in previous message: I meant |
I ran into this problem with this code: from tkinter.filedialog import askopenfilename
import tkinter as tk
def f(e):
print(root.focus_get())
root = tk.Tk()
root.bind("<FocusOut>", f)
button = tk.Button(root, command=askopenfilename, text="click me")
button.pack()
root.mainloop() The code raises a Using this to investigate: widgets = set()
def g():
widget = root.tk.call('focus')
widgets.add(str(widget))
root.after(10, g)
g() I get that on Windows, >>> widgets
{'', '.__tk_filedialog.contents.f2.cancel', '.', '.__tk_filedialog.contents.f2.ent', '.__tk_filedialog'} |
* Renamed `NoteBook` to `Notebook` * Fixed a bug caused by cpython's implementation of tkinter: python/cpython#88758 * Fixed a bug in popup centre * Fixed a bug in `Notebook` where renaming a selected tab will not resize the notch * Fixed a bug in `Notebook` where renaming to the same name will do a lot of work * `slave.py` now accepts `cd` commands * `Terminal`, `TerminalFrame`, and `TerminalTk` now can report if they are running or dead. * `TerminalTk` now has a `send_ping` method which waits for the pong before returning * Now commands that ended will not write "=== Process Ended [<exit_code>] ===" to the screen.
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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