Simple curses GUI in 100 lines.

CustomManu.py

import curses

class Entry:
    def __init__(self, text, fn, x_offset=0, y_offset=0, left_fn=None, right_fn=None) -> None:
        self.text = text
        self.fn = fn
        self.x_pos_offset = x_offset
        self.y_pos_offset = y_offset
        self.left_fn = left_fn
        self.right_fn = right_fn

class Decoration:
    def __init__(self, text="-", n=3, x=0, y=0) -> None:
        self.text = text*n
        self.x = x
        self.y = y
        pass

class Menu:
    screen = curses.initscr()
    curses.noecho()
    screen.keypad(1)
    def __init__(self, title=None) -> None:
        self.entries = []
        self.decorations = []
        self.position = 0
        self.running = False
        self.title = title
        self.pointer = ">"
    
    def add_entry(self, text, fn=None, x_offset=0, y_offset=0) -> int:
        self.entries += [Entry(text, fn, x_offset, y_offset)]
        return len(self.entries) - 1
    
    def add_decoration(self, text="-", n=3, x=0, y=0) -> None:
        self.decorations += [Decoration(text, n, x, y)]

    # Go to main loop here
    def show(self) -> None:
        self.__render_menu()
        g = None
        self.running = True
        while self.running:
            g = self.screen.getch()
            if (g == curses.KEY_UP):
                if (self.position - 1 < 0):
                    self.position = len(self.entries) - 1
                else:
                    self.position -= 1
                self.__render_menu()
            if (g == curses.KEY_DOWN):
                if (self.position + 1 > len(self.entries) - 1):
                    self.position = 0
                else:
                    self.position += 1
                self.__render_menu()
            if (g == curses.KEY_LEFT):
                self.__trigger_function(self.entries[self.position].left_fn)
            if (g == curses.KEY_RIGHT):
                self.__trigger_function(self.entries[self.position].right_fn)
            # Enter is 10 here as well lol
            if (g == 10):
                self.__trigger_function(self.entries[self.position].fn)
        pass

    def terminate(self) -> None:
        curses.echo(1)
        curses.endwin()

    ## Internal methods
    def __trigger_function(self, fn) -> None:
        try:
            fn(self.position)
        except TypeError:
            try:
                fn()
            except TypeError:
                pass
        self.__render_menu()

    def __screen_cleanup(self) -> None:
        self.screen.clear()
        self.screen.refresh()
    
    def __disable_curses(self) -> None:
        curses.endwin()
    
    def __render_decorations(self) -> None:
        for deco in self.decorations:
            self.screen.addstr(deco.y+(-1 if self.title is None else 0)+1, deco.x, deco.text)

    def __render_menu(self) -> None:
        self.screen.clear()
        self.__render_decorations()
        if len(self.entries) > 0:
            c = 0
            c_offset = 0
            if not(self.title is None):
                c_offset += 1
                self.screen.addstr(0, 0, self.title)
            for entry in self.entries:
                if self.position == c:
                    self.screen.addstr(c+c_offset+entry.y_pos_offset, 0+entry.x_pos_offset, self.pointer)
                self.screen.addstr(c+c_offset+entry.y_pos_offset, 2+entry.x_pos_offset, entry.text)
                c += 1
        self.screen.refresh()

### Testing goes here ###
if __name__ == "__main__":
    # Initialization with optional title
    m = Menu("Choose something")
    # Switching buttons
    def a(pos):
        if m.entries[pos].text == "yay":
            m.entries[pos].text = "no"
        else:
            m.entries[pos].text = "yay"
    m.add_entry("yay", a)
    m.add_entry("more")
    m.add_entry("even more")
    # Removing the title
    def d(pos):
        if m.title:
            m.title = None
            m.entries[pos].text = "add stupid title"
        else:
            m.title = "Choose something"
            m.entries[pos].text = "remove stupid title"
    tmp_y = m.add_entry("remove stupid title", d)
    # Decorations
    #   Adding 1 and 2 since tmp_y is the y position of the last entry
    m.add_decoration("* ", 10, 0, tmp_y+1)
    m.add_decoration("* ", 10, 0, tmp_y+2)
    # Offsetting the entries, x=2, y=2, since we finished on the +2 offset in the decorations.
    # Can be anything though.
    m.add_entry("this is slanted", None, 2, 2)
    m.add_entry("more here", None, 2, 2)

    # Show the menu, this goes to the main event loop, blocking the execution.
    m.show()
    # Once done, terminate curses and revert the terminal to default state.
    m.terminate()