With the release of Version 4.0.0, the project is now officially known as "Reskinner". This is a re-write, focusing on improvements to the structure and API of the project.

• Full support for FreeSimpleGUI is here. Thanks to @deajan for the contribution and bringing it to my notice.
• The entire project has been rewritten from scratch for better maintainability, extensibility, and performance.
• The animated_reskin function is no more... because the reskin function itself has animation parameters baked in now.
• The API for reskin has been improved to require only 2 parameters; the window, and the desired theme.
• The project's minimum supported Python version is now 3.8. Python 3.7 support is back from 4.0.1
• Mentions of HSV interpolation in the code have been corrected; it's HSL.

Reskinner is a powerful library for PySimpleGUI and FreeSimpleGUI, enabling dynamic theme switching at runtime without window recreation. It provides a seamless way to update your application's look and feel on the fly.

• Dynamic theme switching without window recreation
• Supports both PySimpleGUI and FreeSimpleGUI
• Easy integration with existing applications
• Precise control over theme transitions with animations and 3 supported interpolation modes.
• Lightweight and dependency-minimal

# For PySimpleGUI
pip install "reskinner[psg]"

# For FreeSimpleGUI
pip install "reskinner[fsg]"

# Install uv if not already installed
pip install uv

# For PySimpleGUI
uv add reskinner[psg]

# For FreeSimpleGUI
uv add reskinner[fsg]

from random import choice
import PySimpleGUI as sg  # or import FreeSimpleGUI as sg
from reskinner import reskin

# Create a simple window
layout = [
    [sg.Text("Hello, Reskinner!")],
    [sg.Button("Change Theme"), sg.Button("Exit")]
]

window = sg.Window("Reskinner Demo", layout)

themes = sg.theme_list()
current_theme = sg.theme()

def change_theme():
    new_theme = choice([t for t in themes if t != current_theme])
    reskin(window, new_theme)
    return new_theme

while True:
    event, values = window.read()

    if event in (sg.WIN_CLOSED, 'Exit'):
        break

    if event == "Change Theme":
        current_theme = change_theme()

window.close()

from reskinner import reskin
import PySimpleGUI as sg

# Apply a new theme instantly
reskin(window=my_window, new_theme="DarkBlue3", theme_function=sg.theme)

Reskinner supports three different interpolation modes for theme transitions; hsl, hue, and rgb (default):

from reskinner import reskin
import PySimpleGUI as sg

# Smooth, animated color transition using HSL interpolation
reskin(
    window=window,
    new_theme="DarkAmber",
    theme_function=sg.theme,
    duration_in_milliseconds=800,
    interpolation_mode="hsl",
)

Customize whether specific elements are styled during reskinning:

from reskinner import reskin
import PySimpleGUI as sg

# Skip elements you don't want to restyle
reskin(
    window=window,
    new_theme="LightGreen",
    theme_function=sg.theme,
    element_filter=lambda e: e.key != "skip_me"
)

This uses one of Reskinner’s built-in easing functions (based on https://easing.net) for a smooth, natural animation.

from reskinner import reskin
import PySimpleGUI as sg

# Apply a theme with animation and built-in easing
reskin(
    window=window,
    new_theme="DarkBlue",
    duration=1000,  # milliseconds
    interpolation_mode="rgb",
    easing_function="ease_in_out_sine",
)

Any callable accepting a float between 0 and 1, and returning a float in the same range, is valid as a custom easing function. In this example, we use the golden ratio as our easing function

from math import pow
from reskinner import reskin
import PySimpleGUI as sg


def golden_ease_out(t: float) -> float:
    phi = (1 + 5 ** 0.5) / 2  # ≈ 1.618
    return 1 - pow(1 - t, phi)

# Apply a theme with golden-ratio-based easing
reskin(
    window=window,
    new_theme="DarkGreen5",
    duration=1000,
    interpolation_mode="rgb",
    easing_function=golden_ease_out,
)

• Python 3.8+
• PySimpleGUI 4.60.0+ or FreeSimpleGUI 5.0.0+ (Tkinter variant only; Reskinner doesn't support *Qt, *Wx, or *Web variants)
• Tkinter (included with Python)

This project is licensed under the MIT License - see the LICENSE file for details.

• The PySimpleGUI and FreeSimpleGUI communities
• All contributors who have helped improve Reskinner

Reskinner runs through each element in a window, then by relying on the element.widget interface to access the underlying Tkinter object, it applies style changes to the window.

Like Unda, I created Reskinner to be a part/feature of a desktop application which I'm developing, however, I decided to open-source it, as I imagined other developers would find such functionality useful in their projects as well.

Development began on Monday 15th August 2022.

I didn't want it to go against the built-in conventions of theme and look_and_feel that PySimpleGUI has.