game.py

#:/usr/bin/env python3

from string import ascii_uppercase
from random import choice

from kivy.core.window import Window
from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ObjectProperty, ListProperty, NumericProperty
from kivy.clock import Clock
from kivy.factory import Factory as F

KV = '''
#:import sin math.sin
#:import RGBA kivy.utils.rgba

FloatLayout:
    Grid:
        id: grid
        grid_size: 5, 5
        pos_hint: {'center': (.5, .5)}

<Cell>:
    active: app.current_cell == self
    color: RGBA('#000000')
    font_size: 20
    background_color:
        (
        '#000000' if self.disabled else
        '#FFFFFF' if self.active else
        '#BBBBBB'
        )

    on_touch_down:
        if self.collide_point(*args[1].pos): app.current_cell = self

    canvas.before:
        Color:
            rgba: RGBA(self.background_color or '#FFFFFF')
        Rectangle:
            size: self.size
            pos: self.pos

        Color:
            rgba:
                (
                RGBA('#000000')[:3] +
                [(sin(app.time * 16) * .25 + .5) if self.active else 1]
                )
        Line:
            rectangle: self.pos + self.size
            width: 2


<Grid>:
    size_hint: None, None
    rows: self.grid_size[0] + 1
    cols: self.grid_size[1] + 1
    width: (self.cols or 1) * 50
    height: (self.rows or 1) * 50

'''

class Game(App):
    current_cell = ObjectProperty(None)
    time = NumericProperty(0)

    def build(self):
        Window.bind(on_key_down=self.handle_key)
        Clock.schedule_interval(self.update_time, 0)
        return Builder.load_string(KV)

    def update_time(self, dt):
        self.time += dt

    def handle_key(self, win, code, scan, letter, modifiers):
        print(code)
        if self.current_cell:
            grid = self.root.ids.grid
            index = grid.children[::-1].index(self.current_cell)
            row, col = divmod(index, grid.cols)

            if letter:
                self.current_cell.text = letter
            elif code == 8:
                # backspace
                self.current_cell.text = ''

            elif code == 273:
                # UP
                row -= 1
            elif code == 274:
                # DOWN
                row += 1
            elif code == 275:
                # RIGHT
                col += 1
            elif code == 276:
                # LEFT
                col -= 1

            if col >= grid.cols:
                col = 1

            elif col < 1:
                col = grid.cols - 1

            if row >= grid.rows:
                row = 1

            elif row < 1:
                row = grid.rows - 1

            index = grid.cols * row + col
            self.current_cell = grid.children[::-1][index]


class Cell(F.Label):
    pass


class Grid(F.GridLayout):
    grid_size = ListProperty([5, 5])

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        width, height = self.grid_size
        # empty corner
        self.add_widget(F.Widget())

        # top row for letters
        for _, L in zip(range(width), ascii_uppercase):
            self.add_widget(F.Label(text=L))

        for Y in range(height):
            # first column for numbers
            self.add_widget(F.Label(text=str(Y)))
            for X in range(width):
                self.add_widget(
                    F.Cell(
                        disabled=choice(
                            [False] * 10 + [True]
                        )
                    )
                )


if __name__ == '__main__':
    Game().run()