Python type alias example

type_aliases.ipynb

{
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   "cell_type": "code",
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   "source": [
    "from math import sqrt\n",
    "from typing import List, Generic, TypeVar\n",
    "\n",
    "T = TypeVar('T', int, float)\n",
    "\n",
    "class Point(Generic[T]):\n",
    "    def __init__(self, x: T, y: T) -> None:\n",
    "        self.px = x # type: T\n",
    "        self.py = y # type: T\n",
    "        \n",
    "    @property\n",
    "    def x(self) -> T:\n",
    "        return self.px\n",
    "    \n",
    "    @property\n",
    "    def y(self) -> T:\n",
    "        return self.py\n",
    "    \n",
    "    def distance_point_coordinates(self, px: T, py: T) -> float:\n",
    "        x_diff = self.px - px\n",
    "        y_diff = self.py - py\n",
    "        return sqrt( x_diff*x_diff + y_diff*y_diff )\n",
    "\n",
    "    def distance(self, point: 'Point') -> float:\n",
    "        x_diff = self.px - point.x\n",
    "        y_diff = self.py - point.y\n",
    "        return sqrt( x_diff*x_diff + y_diff*y_diff )\n",
    "\n",
    "    def __str__(self) -> str:\n",
    "        return '({}, {})'.format(self.px, self.py)\n",
    "\n",
    "    def __repr__(self) -> str:\n",
    "        return 'Point({}, {})'.format(self.px, self.py)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(1, 1)\n",
      "(4, 2)\n",
      "3.1622776601683795\n",
      "3.1622776601683795\n",
      "[Point(1, 1), Point(4, 2)]\n"
     ]
    }
   ],
   "source": [
    "p1 = Point(1, 1)\n",
    "p2 = Point(4, 2)\n",
    "\n",
    "print(p1)\n",
    "print(p2)\n",
    "print(p1.distance_point_coordinates(p2.x, p2.y))\n",
    "print(p2.distance(p1))\n",
    "\n",
    "polyline = [] # type: List[Point]\n",
    "polyline.append(p1)\n",
    "polyline.append(p2)\n",
    "print(polyline)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[Point(1, 1), Point(4, 2), 'point']\n"
     ]
    }
   ],
   "source": [
    "polyline.append(\"point\")\n",
    "print(polyline)"
   ]
  }
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