An attempt to make a flexbox-like manager in Tkinter

flexbox.py

import sys
from tkinter import Event, Tk
from tkinter.ttk import Button, Frame, Widget
from typing import Literal

FlexboxMode = Literal["horizontal", "vertical"]


class Flexbox(Frame):
    def __init__(
        self,
        *args,
        mode: FlexboxMode = "horizontal",
        **kwargs,
    ):
        super().__init__(*args, **kwargs)

        self.__mode: FlexboxMode = mode
        self.__widgets: list[Widget] = []
        self.__refreshed = False

        self.bind("<Configure>", self.__on_configure)
        self.bind("<<FlexboxChange>>", self.__on_flexbox_change)

    @property
    def mode(self) -> FlexboxMode:
        return self.__mode

    @mode.setter
    def mode(self, mode: FlexboxMode) -> None:
        self.__mode = mode
        self.event_generate("<<FlexboxChange>>")

    def add(self, widget: Widget) -> None:
        self.__widgets.append(widget)
        self.event_generate("<<FlexboxChange>>")

    def remove(self, widget: Widget) -> None:
        self.__widgets.remove(widget)
        self.event_generate("<<FlexboxChange>>")

    def __on_configure(self, event: Event) -> None:
        self.__refresh(event.width, event.height)

    def __on_flexbox_change(self, event: Event) -> None:
        self.__refresh()

    def __refresh(self, width: int | None = None, height: int | None = None) -> None:
        def add_widget_length(widget: Widget) -> None:
            nonlocal length

            widget.grid(row=row, column=column)
            bbox = self.grid_bbox(row=row, column=column)
            assert bbox is not None

            if horizontal:
                length += bbox[2]
            else:
                length += bbox[3]

        def is_first_widget() -> bool:
            return horizontal and column == 0 or not horizontal and row == 0

        def show_widget(widget: Widget) -> None:
            nonlocal column, i, row

            # Widget is already mapped by add_widget_length()
            # widget.grid(row=row, column=column)

            if horizontal:
                column += 1
            else:
                row += 1
            i += 1

        def move_to_next_line() -> None:
            nonlocal column, length, row

            length = 0
            if horizontal:
                row += 1
                column = 0
            else:
                row = 0
                column += 1

        width = width or self.winfo_width()
        height = height or self.winfo_height()

        # Prevent excessive refreshing in one frame
        if self.__refreshed:
            return
        elif width <= 1 or height <= 1:
            # JANK: probably not rendered yet, need to wait
            self.after(50, self.__refresh)
            return
        else:
            self.__refreshed = True
            self.after(16, self.__unset_refresh)

        horizontal = self.mode != "vertical"
        max_length = width if horizontal else height

        widgets = self.__widgets.copy()
        i = 0
        row = 0
        column = 0
        length = 0

        while i < len(widgets):
            widget = widgets[i]
            add_widget_length(widget)
            if length <= max_length or is_first_widget():
                show_widget(widget)
            else:
                move_to_next_line()

    def __unset_refresh(self) -> None:
        self.__refreshed = False


def switch_flexbox_mode(mode: FlexboxMode | None = None):
    if mode is None:
        mode = "vertical" if flexbox.mode == "horizontal" else "horizontal"
    flexbox.mode = mode
    app.title(f"Flexbox Demo ({mode.capitalize()})")


# Make example look prettier on windows
if sys.platform == "win32":
    from ctypes import windll

    windll.shcore.SetProcessDpiAwareness(2)

app = Tk()
app.geometry("640x480")
app.grid_columnconfigure(0, weight=1)
app.grid_rowconfigure(0, weight=1)

flexbox = Flexbox(app)
switch_flexbox_mode("horizontal")
flexbox.grid(sticky="nesw")

for i in range(10):
    button = Button(
        flexbox,
        text=f"Button {i+1}",
        padding=i * 10,
        command=switch_flexbox_mode,
    )
    flexbox.add(button)

app.mainloop()