Public Protected Private Variables

PublicProtectedPrivate.ipynb

{
 "cells": [
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In Python, the scope ( Public, Protected, Private) characteristic of an attribute or member of the class is indicated by \"the naming conventions of the member\". These are the naming conventions\n",
    "\n",
    "**Public**: This means the member can be accessed outside of the class by other instances. \n",
    "        The naming convention denotes that it has no underscores eg numberOfFields = 6\n",
    "**Protected**: This means that the member can be accessed by the Parent Class and its \"Children\" - those classes that inherit the parent class\n",
    "        The naming convention denotes that it has **ONE underscore in front of the member name** eg _numberOfFields = 6\n",
    "**Private** This means the member is only accessible within the parent class. \n",
    "            The naming convention denotes that it has TWO underscores in front of the member name eg __numberOfFields = 6\n",
    "            \n",
    "            \n",
    "Lets check some examples"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Car:\n",
    "    numberOfWheels = 4\n",
    "    _colour = \"Black\"  #protected attribute\n",
    "    __yearOfManufacture = '2017' ## private"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "class BMW(Car):\n",
    "    def __init__(self):\n",
    "        print(\"Protected attribute colour of car is :{} and the car has {}\".format(self._colour, self.numberOfWheels))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Lets instantiate both classes and see how the attributes behave"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Public attribute 4\n"
     ]
    }
   ],
   "source": [
    "car = Car()\n",
    "print(\"Public attribute {}\".format(car.numberOfWheels))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Protected attribute colour of car is :Black and the car has 4\n"
     ]
    }
   ],
   "source": [
    "bmw = BMW()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Lets access the private variable outside of the class"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "Car instance has no attribute '__yearOfManufacture'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-21-f33c89bb066a>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Accessing the private variable: \"\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mcar\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0m__yearOfManufacture\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mAttributeError\u001b[0m: Car instance has no attribute '__yearOfManufacture'"
     ]
    }
   ],
   "source": [
    "print(\"Accessing the private variable: \", car.__yearOfManufacture)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Though we are strongly advised not to use the private variable outside of the class we can actually access it like below"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "('Accessing the private variable YearOfManufacture: ', '2017')\n"
     ]
    }
   ],
   "source": [
    "print(\"Accessing the private variable YearOfManufacture: \", car._Car__yearOfManufacture)"
   ]
  }
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