Add point example

Author: gjbex

source-code/object-orientation/attr_intro.ipynb

@@ -1387,6 +1387,223 @@
    "source": [
     "Of course, you can still impliment your own hash method and comparison methods if required."
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "536b220c-b157-47de-89e6-f4a4946e480c",
+   "metadata": {},
+   "source": [
+    "# Example"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "6e2c5118-2211-4487-9055-592b89b5b559",
+   "metadata": {},
+   "source": [
+    "We will implement the `Point` class that was sued as a running example."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 62,
+   "id": "391732ee-8952-49e6-857c-e8b8c6e8dab4",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from math import sqrt"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 80,
+   "id": "2faf536d-83eb-4587-8116-4d665e1cf546",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "@attr.s\n",
+    "class Point:\n",
+    "    x: float = attr.ib(converter=float)\n",
+    "    y: float = attr.ib(converter=float)\n",
+    "        \n",
+    "    def distance(self, other):\n",
+    "        return sqrt((self.x - other.x)**2 + (self.y - other.y)**2)\n",
+    "    \n",
+    "    @property\n",
+    "    def coords(self):\n",
+    "        return (self.x, self.y)\n",
+    "    \n",
+    "    @coords.setter\n",
+    "    def coords(self, value):\n",
+    "        self.x, self.y = value"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 68,
+   "id": "62516ade-9c73-4cb1-8143-110c5141c672",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(Point(x=3.1, y=5.0), Point(x=3.2, y=1.9))"
+      ]
+     },
+     "execution_count": 68,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p1, p2 = Point(3.1, 5), Point('3.2', 1.9)\n",
+    "p1, p2"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "b1d56498-9adc-4ac3-bdde-1b331414c587",
+   "metadata": {},
+   "source": [
+    "Note the differences with the original \"pure Python\" implementation:\n",
+    "* `x` and `y` are public attributes, and\n",
+    "* values assigned to the attributes are not validated."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 71,
+   "id": "a606d9c1-e392-462b-8420-e88f4735896a",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "Point(x='abc', y=5.0)"
+      ]
+     },
+     "execution_count": 71,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p1.x = 'abc' \n",
+    "p1"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "c4b80743-aad7-4ae2-98d8-c422440ea9cf",
+   "metadata": {},
+   "source": [
+    "If you want that level of control, the advantages of using `attrs` start to decrease considerably."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 74,
+   "id": "2daae99c-7ebb-4dab-95a5-edc5984bcdbc",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "Point(x=17.1, y=12.5)"
+      ]
+     },
+     "execution_count": 74,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p1.coords = 17.1, 12.5\n",
+    "p1"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "c4ce5a9c-568c-4c86-be22-9b8f08ec5bda",
+   "metadata": {},
+   "source": [
+    "## Inheritance"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ac2f90f5-3d5e-4dd4-9fe2-4fa56f669ced",
+   "metadata": {},
+   "source": [
+    "Inheritance simply works as expected.  Methods and attributes can be added to subclasses."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 75,
+   "id": "1a6a3c6d-d177-4f4f-b339-9ba3be1ae264",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "@attr.s\n",
+    "class PointMass(Point):\n",
+    "    mass: float = attr.ib(converter=float)\n",
+    "    \n",
+    "    def __attr_pre_init__(self)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 78,
+   "id": "52e32576-1c2b-4195-868f-4505da5e141e",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "PointMass(x=1.2, y=2.3, mass=5.0)"
+      ]
+     },
+     "execution_count": 78,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p1 = PointMass(1.2, 2.3, 5.0)\n",
+    "p1"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 82,
+   "id": "f40178b8-338d-4afd-95e2-f3b8a6afcc2e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "p2 = Point(3.2, 4.1)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 83,
+   "id": "bd49b807-7255-408b-9989-1212f6e8c1df",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "2.690724809414742"
+      ]
+     },
+     "execution_count": 83,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p1.distance(p2)"
+   ]
   }
  ],
  "metadata": {