attribute_and_property_overrides.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "ee258d3c",
   "metadata": {},
   "outputs": [],
   "source": [
    "class Example:\n",
    "    data = 'this is data attribute'\n",
    "    @property\n",
    "    def prop(self):\n",
    "        return 'this is property'"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "14ffc5e7",
   "metadata": {},
   "source": [
    "## Override of data attribute"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "e6f52904",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "obj = Example()\n",
    "\n",
    "# This obj does not have any instance attributes\n",
    "vars(obj) == obj.__dict__ == {}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "ec43c1d0",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Override data attribute\n",
    "obj.data = 'overrided'\n",
    "obj.data == 'overrided' and vars(obj) == {'data': 'overrided'}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "34c76d21",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is data attribute'"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Class data attribue still remains\n",
    "Example.data"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ca592fd5",
   "metadata": {},
   "source": [
    "## Override of property"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "e9b465bc",
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "can't set attribute",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-5-f8edd667f4b4>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      2\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      3\u001b[0m \u001b[0;31m# Cannot set property without a setter\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 4\u001b[0;31m \u001b[0mobj\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mprop\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'overrided'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: can't set attribute"
     ]
    }
   ],
   "source": [
    "obj = Example()\n",
    "\n",
    "# Cannot set property without a setter\n",
    "obj.prop = 'overrided'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "80ff05a0",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is property'"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Manually set the data attribute by patch the __dict__\n",
    "obj.__dict__['prop'] = 'overrided'\n",
    "# Getter of the property still exists\n",
    "obj.prop"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "69274da2",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'overrided'"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Destroy the property, or use `del`\n",
    "Example.prop = 'something else'\n",
    "# obj.prop no longer a property, its value now came from the instance's attributes\n",
    "obj.prop"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d255cdf8",
   "metadata": {},
   "source": [
    "## Override attribute with created property"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "087e09fd",
   "metadata": {},
   "outputs": [],
   "source": [
    "obj = Example()\n",
    "obj.val = 'this is instance data attribute'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "8f5b554c",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'overrided by property'"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Example.val = property(lambda self: 'overrided by property')\n",
    "# Now it reads from property\n",
    "obj.val"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "04bfce79",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is instance data attribute'"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Destroy the property\n",
    "del Example.val\n",
    "# Now its read from instance attribute again\n",
    "obj.val"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "310499bc",
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.8.10"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 5
}