ВНЕСИ предложеные тобой улучшения, которые можно внести для оптимальности и качества кода.
from tkinter import *
from tkinter import ttk, filedialog, messagebox
from PIL import Image, ImageTk, ImageGrab

class ImprovedImageApp:
    def __init__(self, master):
        self.image_key_dict = {}
        self.saved_images = []

        master.title("Improved Image App")
        master.resizable(False, False)

        self.init_widgets(master)
        self.init_bindings(master)

    def init_widgets(self, master):
        self.init_canvas(master)
        self.init_menu(master)
        self.init_toolbar(master)

    def init_canvas(self, master):
        self.left_canvas = Canvas(master, width=320, height=320, relief=RIDGE, bd=3)
        self.right_canvas = Canvas(master, width=320, height=320, relief=RIDGE, bd=3)

        self.left_canvas.grid(row=0, column=0, padx=10, pady=10)
        self.right_canvas.grid(row=0, column=1, padx=10, pady=10)

    def init_menu(self, master):
        self.menu_bar = Menu(master)
        master.config(menu=self.menu_bar)

        file_menu = Menu(self.menu_bar, tearoff=0)
        file_menu.add_command(label="Открыть", command=self.open_file)
        file_menu.add_command(label="Выход", command=master.quit)
        self.menu_bar.add_cascade(label="Файл", menu=file_menu)

    def init_toolbar(self, master):
        self.toolbar = ttk.Frame(master, padding=5, borderwidth=1)

        open_button = ttk.Button(self.toolbar, text="Открыть", command=self.open_file)
        open_button.pack(side=LEFT, padx=2)

        save_button = ttk.Button(self.toolbar, text="Сохранить", command=self.save_image)
        save_button.pack(side=LEFT, padx=2)

        undo_button = ttk.Button(self.toolbar, text="Отменить последнее действие", command=self.undo_last_action)
        undo_button.pack(side=LEFT, padx=2)

        self.toolbar.grid(row=1, column=0, columnspan=2, sticky=W+E)

    def init_bindings(self, master):
        master.bind('o', self.open_key_dialog)

    def open_file(self):
        file_path = filedialog.askopenfilename(
            filetypes=(("Изображения", "*.jpg;*.png"), ("Все файлы", "*.*")))

        if file_path:
            self.open_resize_dialog(file_path)

    def open_resize_dialog(self, file_path):
        resize_dialog = Toplevel()
        resize_dialog.title("Изменение размера изображения")
        resize_dialog.resizable(False, False)

        size_var = StringVar(value="256")
        size_entry = ttk.Entry(resize_dialog, textvariable=size_var, width=10)
        size_entry.pack(side=LEFT, padx=5, pady=10)

        dimension_label = ttk.Label(resize_dialog, text="px", padding=(0, 0, 5, 0))
        dimension_label.pack(side=LEFT)

        resize_button = ttk.Button(
            resize_dialog, text="Изменить размер",
            command=lambda: self.resize_image(file_path, size_var.get()))
        resize_button.pack(side=LEFT, padx=10, pady=10)

    def resize_image(self, file_path, new_size):
        try:
            new_size = int(new_size)
        except ValueError:
            messagebox.showerror("Ошибка", "Введите целое число в поле ввода.")
            return

        with Image.open(file_path) as image:
            image = image.convert("RGB").resize((new_size, new_size))

        photo = ImageTk.PhotoImage(image)
        key = file_path.split("/")[-1]
        self.image_key_dict[key] = photo
        self.saved_images.append(dict(key=key, photo=photo))
        self.display_images()

    def save_image(self):
        file_path = filedialog.asksaveasfilename(
            defaultextension=".png", filetypes=(("PNG file", "*.png"),))

        if file_path:
            x, y = self.right_canvas.winfo_rootx(), self.right_canvas.winfo_rooty()
            x += self.right_canvas.winfo_x()
            y += self.right_canvas.winfo_y()
            x1 = x + self.right_canvas.winfo_width()
            y1 = y + self.right_canvas.winfo_height()

            ImageGrab.grab().crop((x, y, x1, y1)).save(file_path)

            for i, image in enumerate(self.saved_images):
                if image["key"] in file_path:
                    del self.saved_images[i]
                    break

    def display_images(self):
        self.left_canvas.delete(ALL)
        self.right_canvas.delete(ALL)

        x, y = 0, 0
        for key, photo in self.image_key_dict.items():
            self.left_canvas.create_image(x, y, anchor=NW, image=photo)
            self.right_canvas.create_image(x, y, anchor=NW, image=photo)
            x += photo.width() + 10
            y += photo.height() + 10

    def open_key_dialog(self, event=None):
        key_dialog = Toplevel()
        key_dialog.title("Выбор символа/ключа")
        key_dialog.resizable(False, False)

        message_label = ttk.Label(
            key_dialog, text="Введите символ/ключ для изображения:", padding=(0, 0, 5, 0))
        message_label.pack(side=LEFT, padx=5, pady=10)

        key_var = StringVar(value="")
        key_entry = ttk.Entry(key_dialog, textvariable=key_var, width=20)
        key_entry.pack(side=LEFT, padx=5, pady=10)

        file_button = ttk.Button(
            key_dialog, text="Выбрать файл",
            command=lambda: self.open_file_key(key_var))
        file_button.pack(side=LEFT, padx=10, pady=10)

    def open_file_key(self, key_var):
        file_path = filedialog.askopenfilename(
            filetypes=(("Изображения", "*.jpg;*.png"), ("Все файлы", "*.*")))

        if file_path:
            key = key_var.get()
            if key:
                if key in self.image_key_dict:
                    self.change_image(key, file_path)
                else:
                    photo = ImageTk.PhotoImage(
                        Image.open(file_path).convert("RGB").resize((256, 256)))
                    self.image_key_dict[key] = photo
                    self.saved_images.append(dict(key=key, photo=photo))
                    self.display_images()
            else:
                messagebox.showwarning("Внимание", "Введите символ/ключ для изображения.")

    def change_image(self, key, file_path):
        photo = ImageTk.PhotoImage(
            Image.open(file_path).convert("RGB").resize((256, 256)))

        self.image_key_dict[key] = photo
        self.display_images()

    def undo_last_action(self):
        if self.saved_images:
            last_image = self.saved_images.pop()
            del self.image_key_dict[last_image["key"]]
            self.display_images()

if __name__ == "__main__":
    root = Tk()
    app = ImprovedImageApp(root)
    root.mainloop()

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