Fix Tkinter ttk.Button image toggle: compare state with str(), keep PhotoImage refs, consider a Checkbutton

Troubleshoot a Tkinter ttk.Button that toggles images only with print. Cast state to str(), keep PhotoImage refs, and use a Checkbutton for persistent toggles.

Toggle a Tkinter button image on click sounds trivial, yet a common pitfall appears when you read the widget state from a ttk.Button. The symptom looks odd: the callback works only when a print call is present. Remove the print, and the logic stops toggling as intended. The fix is simple once you know what Tkinter is handing you under the hood.

Problem setup

Imagine a button rendered as an image. On click, the image should switch and remain until the next click. The following snippet illustrates that setup and the odd dependency on print:

from tkinter import *
from tkinter import ttk

def flip_visual():
    print(toggle_btn["state"])  # works with this line present
    if toggle_btn["state"] == "normal":
        pic_obj = PhotoImage(file="test1.png")
        toggle_btn.configure(image=pic_obj)
        toggle_btn.image = pic_obj
        toggle_btn.configure(state="active")
    elif toggle_btn["state"] == "active":
        pic_obj = PhotoImage(file="test.png")
        toggle_btn.configure(image=pic_obj)
        toggle_btn.image = pic_obj
        toggle_btn.configure(state="normal")

app = Tk()
app.geometry("600x600")

pic_obj = PhotoImage(file="test.png")
toggle_btn = ttk.Button(app, text="TEST", image=pic_obj, command=flip_visual)
toggle_btn.pack(anchor="center")

app.mainloop()

What’s really going on

The culprit is in the conditional checks. For ttk widgets, reading a configuration option like state returns a Tcl object, not a plain Python string. In other words, toggle_btn["state"] is not "normal" or "active" as a str. If you inspect the type, you’ll see something like <class '_tkinter.Tcl_Obj'> instead of str. Comparing that Tcl object directly to a Python string will not produce the expected result.

The print call is a red herring. It exposes the value but doesn’t solve the underlying type mismatch. To make the conditions reliable, cast the value to a Python string before comparing.

Fix and corrected example

Convert the state to str inside the conditionals. The rest of the logic remains the same, including image swapping and reference retention to avoid garbage collection:

from tkinter import *
from tkinter import ttk

def flip_visual():
    if str(toggle_btn["state"]) == "normal":
        pic_swap = PhotoImage(file="test1.png")
        toggle_btn.configure(image=pic_swap)
        toggle_btn.image = pic_swap
        toggle_btn.configure(state="active")
    elif str(toggle_btn["state"]) == "active":
        pic_swap = PhotoImage(file="test.png")
        toggle_btn.configure(image=pic_swap)
        toggle_btn.image = pic_swap
        toggle_btn.configure(state="normal")

app = Tk()
app.geometry("600x600")

pic_initial = PhotoImage(file="test.png")
toggle_btn = ttk.Button(app, text="TEST", image=pic_initial, command=flip_visual)
toggle_btn.pack(anchor="center")

app.mainloop()

This change makes the check deterministic without relying on any print call.

About the "active" state

It’s also worth understanding the meaning of state values in ttk. The active state is associated with the pointer press on the widget and typically reverts when the pointer is released. If your goal is a persistent on/off visual, that’s semantically closer to a selection state rather than an interaction state. A practical approach is to use a ttk.Checkbutton with a custom style and set one image for the selected state and another for the !selected state. This gives a stable toggle without overloading interaction states. For ideas, see examples of custom styles for checkbuttons in ttk-focused resources.

Why this matters

GUI code often hinges on small assumptions about types and states. Mixing ttk and tk patterns can be deceptive because attribute access looks identical while the underlying objects differ. Explicitly converting values to strings when comparing widget states eliminates hard-to-trace edge cases. Understanding the semantic intent of states like active versus selected also prevents subtle UI logic bugs.

Takeaways

When reading ttk widget options such as state, compare against strings only after casting the value via str(...). Keep a persistent reference to images assigned to widgets to avoid premature garbage collection. If you need a persisted toggle instead of a press-feedback state, consider a ttk.Checkbutton with a custom style mapping images to selected and !selected. For additional background on reading widget states, you can check resources discussing state retrieval in Tkinter, such as community Q&A focused on this exact issue.

A small, explicit cast resolves the immediate problem, and choosing the right widget semantics makes the behavior predictable and maintainable.