GUI temperature converter made in Python using Tk

temperature_converter.py

import tkinter as tk
from typing import Callable, Optional


def is_number_text(text):
    if text in ["", "-"]:
        return True
    try:
        float(text)
        return True
    except ValueError:
        return False


class Conversions:
    @staticmethod
    def f_to_c(x: float) -> float:
        return (x - 32) * 5 / 9

    @staticmethod
    def c_to_f(x: float) -> float:
        return (x * 9 / 5) + 32

    @staticmethod
    def c_to_k(x: float) -> float:
        return x + 273.15

    @staticmethod
    def k_to_c(x: float) -> float:
        return x - 273.15

    @staticmethod
    def f_to_k(x: float) -> float:
        return Conversions.c_to_k(Conversions.f_to_c(x))

    @staticmethod
    def k_to_f(x: float) -> float:
        return Conversions.c_to_f(Conversions.k_to_c(x))


class ReactiveEntry(tk.Entry):
    def __init__(self, *args, on_updated: Callable[[str, str, bool], None], value_check: Callable[[str], bool], **kwargs):
        self.var = tk.StringVar()
        self.last_value = ""
        self.on_updated = on_updated
        self.value_check = value_check
        self.just_set = False
        super().__init__(textvariable=self.var, *args, **kwargs)
        self.var.trace("w", self._var_updated)

    def _var_updated(self, *args):
        new_val = self.var.get()
        if not self.value_check(new_val):
            self.var.set(self.last_value)
            return
        self.on_updated(self.last_value, new_val, not self.just_set)
        self.just_set = False
        self.last_value = new_val

    def set(self, value):
        self.just_set = True
        self.var.set(value)
        self.last_value = value


class App:
    def __init__(self):
        self.root = tk.Tk()
        self.root.title("Temperature Converter")

        self.f_entry: Optional[ReactiveEntry] = None
        self.c_entry: Optional[ReactiveEntry] = None
        self.k_entry: Optional[ReactiveEntry] = None
        self.ui_stuff()

        self.root.mainloop()

    def ui_stuff(self):
        tk.Label(self.root, text="Fahrenheit").pack()
        self.f_entry = ReactiveEntry(self.root, on_updated=self.handle_f_change, value_check=is_number_text)
        self.f_entry.pack()
        tk.Label(self.root, text="Celsius").pack()
        self.c_entry = ReactiveEntry(self.root, on_updated=self.handle_c_change, value_check=is_number_text)
        self.c_entry.pack()
        tk.Label(self.root, text="Kelvin").pack()
        self.k_entry = ReactiveEntry(self.root, on_updated=self.handle_k_change, value_check=is_number_text)
        self.k_entry.pack()

    def handle_f_change(self, before, after, user_change):
        if user_change:
            self.handle_change(after, self.c_entry, Conversions.f_to_c)
            self.handle_change(after, self.k_entry, Conversions.f_to_k)

    def handle_c_change(self, before, after, user_change):
        if user_change:
            self.handle_change(after, self.f_entry, Conversions.c_to_f)
            self.handle_change(after, self.k_entry, Conversions.c_to_k)

    def handle_k_change(self, before, after, user_change):
        if user_change:
            self.handle_change(after, self.f_entry, Conversions.k_to_f)
            self.handle_change(after, self.c_entry, Conversions.k_to_c)

    @staticmethod
    def handle_change(value: str, element: ReactiveEntry, equation: Callable[[float], float]) -> None:
        val = ""
        try:
            value = float(value)
        except ValueError:
            pass
        else:
            val = str(round(equation(value), 1))
        element.set(val)


if __name__ == "__main__":
    App()