{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "6f167dfd",
   "metadata": {},
   "source": [
    "# 18-23 · Gumka\n",
    "\n",
    "Praktyka do sekcji [„Gumka”"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a4ba7d64",
   "metadata": {},
   "source": [
    "## Cel\n",
    "\n",
    "Gumka jako pociągnięcie koloru tła działa tak samo jak ołówek."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b4f3d519",
   "metadata": {},
   "source": [
    "## Pro mainloop() w tym laptopie\n",
    "\n",
    "Zamiast `root.mainloop()` używany tutaj `root.update()` + `root.destroy()` jest takie, że aplikacja jest zbudowana dokładnie tak samo, tylko bez niekończącego się oczekiwania na końcu (zobacz wyjaśnienie w rozdziale 16)."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "16cb8bd2",
   "metadata": {},
   "source": [
    "## Sprawa robocza"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "e8b510df",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2026-09-03T00:52:06.978040Z",
     "iopub.status.busy": "2026-09-03T00:52:06.977915Z",
     "iopub.status.idle": "2026-09-03T00:52:07.097810Z",
     "shell.execute_reply": "2026-09-03T00:52:07.097170Z"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Элементов на холсте: 2\n"
     ]
    }
   ],
   "source": [
    "import tkinter as tk\n",
    "\n",
    "CANVAS_BG = \"#ffffff\"\n",
    "\n",
    "root = tk.Tk()\n",
    "canvas = tk.Canvas(root, width=300, height=200, bg=CANVAS_BG)\n",
    "canvas.pack()\n",
    "\n",
    "canvas.create_line(20, 20, 200, 20, fill=\"black\", width=6)  # \"нарисованная\" линия\n",
    "\n",
    "def steret(x1, y1, x2, y2):\n",
    "    canvas.create_line(x1, y1, x2, y2, fill=CANVAS_BG, width=10, capstyle=tk.ROUND)\n",
    "\n",
    "steret(50, 20, 150, 20)\n",
    "root.update()\n",
    "print(\"Элементов на холсте:\", len(canvas.find_all()))  # линия НЕ удалена, просто перекрыта\n",
    "root.destroy()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "89e34104",
   "metadata": {},
   "source": [
    "## Zadanie niezależne od zadania ★★\n",
    "\n",
    "Sprawdź na prawdziwym oknie: `len(canvas.find_all())` po „wymazaniu”"
   ]
  }
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