Notebook to try out the functionality of `%gui qt`

gui_qt_playground.ipynb

{
 "cells": [
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   "cell_type": "code",
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   "cell_type": "markdown",
   "id": "781e9597",
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   "source": [
    "Case 1:\n",
    "1. Choose a Qt version that isn't installed. \n",
    "2. Choose one that shows as installed"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "cb56d71b",
   "metadata": {},
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "ERROR:root:\n",
      "    Could not load requested Qt binding. Please ensure that\n",
      "    PyQt4 >= 4.7, PyQt5, PySide >= 1.0.3 or PySide2 is available,\n",
      "    and only one is imported per session.\n",
      "\n",
      "    Currently-imported Qt library:                              None\n",
      "    PyQt4 available (requires QtCore, QtGui, QtSvg):            False\n",
      "    PyQt5 available (requires QtCore, QtGui, QtSvg, QtWidgets): True\n",
      "    PySide >= 1.0.3 installed:                                  False\n",
      "    PySide2 installed:                                          False\n",
      "    Tried to load:                                              ['pyqt']\n",
      "    \n"
     ]
    }
   ],
   "source": [
    "%gui qt4\n",
    "%gui qt5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "0b46a30e",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Evaluate here and verify loop is running\n",
    "x = 5"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "17a06336",
   "metadata": {},
   "source": [
    "Case 1b:\n",
    "1. Explicitly set `QT_API` environment variable\n",
    "2. Request a different version"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "cc52542e",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Request for \"qt5\" will be ignored because `QT_API` environment variable is set to \"pyside6\"\n"
     ]
    }
   ],
   "source": [
    "import os\n",
    "os.environ['QT_API'] = 'pyside6'\n",
    "%gui qt5"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d91ad56c",
   "metadata": {},
   "source": [
    "Case 2:\n",
    "1. Start a Qt loop.\n",
    "2. Stop it.\n",
    "3. Restart it."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "698b28d2",
   "metadata": {
    "scrolled": true
   },
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "ad130526",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "97d6e16a",
   "metadata": {
    "scrolled": true
   },
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f0424ce3",
   "metadata": {},
   "source": [
    "Case 3:\n",
    "1. Start a Qt loop.\n",
    "2. Stop it.\n",
    "3. Try to start a different version (won't work due to import mechanics, so we raise an exception)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "4b354e3d",
   "metadata": {
    "scrolled": true
   },
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "f8e91f9c",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "f593894f",
   "metadata": {
    "scrolled": false
   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "ERROR:root:Cannot switch Qt versions for this session; must use qt6.\n"
     ]
    }
   ],
   "source": [
    "%gui qt5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "85885cd3",
   "metadata": {},
   "outputs": [],
   "source": [
    "# OK, request the correct one.\n",
    "%gui qt6"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "057eba0e",
   "metadata": {},
   "source": [
    "Case 3b:\n",
    "1. Start a Qt loop.\n",
    "2. Stop it. Explicitly delete `QT_API` environment variable.\n",
    "3. Try to start a different version (won't work due to import mechanics)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "8dbb05af",
   "metadata": {
    "scrolled": true
   },
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "b5ef0512",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui\n",
    "import os\n",
    "del os.environ['QT_API']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "491829de",
   "metadata": {
    "scrolled": false
   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "ERROR:root:Cannot switch Qt versions for this session; must use qt6.\n"
     ]
    }
   ],
   "source": [
    "%gui qt5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "a51515f9",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c8d9d803",
   "metadata": {},
   "source": [
    "Case 4:\n",
    "1. Request specific version\n",
    "2. Stop it\n",
    "3. Request generic (should proceed just fine)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "f046b851",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "ca31927a",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "d336b548",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui qt"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "24ac69e3",
   "metadata": {},
   "source": [
    "Final test, with actual window."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "de953bd0",
   "metadata": {},
   "outputs": [],
   "source": [
    "%gui qt6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "2372b14c",
   "metadata": {},
   "outputs": [],
   "source": [
    "from typing import List\n",
    "from PySide6.QtWidgets import QApplication, QLabel, QWidget\n",
    "\n",
    "def qt_app() -> QApplication:\n",
    "    app = QApplication.instance()\n",
    "    if app is None:\n",
    "        app = QApplication()\n",
    "    return app\n",
    "\n",
    "\n",
    "no_garbage_collector: List[QWidget] = []\n",
    "\"\"\"\n",
    "Keep all instances of `QWidget` from being garbage-collected by putting them\n",
    "here. If a `QWidget` is not used, they will not be rendered by the event loop.\n",
    "\"\"\"\n",
    "\n",
    "\n",
    "def show_label():\n",
    "    label = QLabel(\"<font color=red size=40>Hello World!</font>\")\n",
    "    label.show()\n",
    "    no_garbage_collector.append(label)\n",
    "    # app.exec()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "1d3649c4",
   "metadata": {},
   "outputs": [],
   "source": [
    "show_label()\n",
    "x = 5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "a409d3b3",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n"
     ]
    }
   ],
   "source": [
    "print(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "e79df8ac",
   "metadata": {},
   "outputs": [],
   "source": [
    "# leaves windows hanging\n",
    "%gui"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "5784598a",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Windows \"wake up\"\n",
    "%gui qt"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "5ce9de66",
   "metadata": {},
   "outputs": [],
   "source": []
  }
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