Ch18-Inheritance.ipynb

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   "source": [
    "# Inheritance\n",
    "<a href=\"https://colab.research.google.com/github/rambasnet/FDSPython-Notebooks/blob/master/Ch18-Inheritance.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>\n",
    "\n",
    "- http://openbookproject.net/thinkcs/python/english3e/inheritance.html\n",
    "- https://www.python-course.eu/python3_inheritance.php\n",
    "\n",
    "- powerful feature that facilitates code reuse mimicking real-world phenomena\n",
    "- ability to define a new class (child) that is modified version of an existing class (parent)\n",
    "- can add new methods and properties to a class without modifying the existing class\n",
    "- some imitation(s) if inheritance:\n",
    "    - can make programs difficult to read\n",
    "    - when method is invoked, it is sometimes not clear where to find its definition esp. in a large project relevant code may be scattered among several modules\n",
    "- see better example (a hand of cards) in the text\n",
    "- syntax:\n",
    "```\n",
    "class childClassName(parentClass1, baseClass2, ...):\n",
    "    #code (attributes and methods)\n",
    "    pass\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Single Inheritance\n",
    "- supported by almost all OOP langauges\n",
    "<img src=\"resources/Inheritance.png\" width=\"100%\">"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 116,
   "metadata": {},
   "outputs": [],
   "source": [
    "# by dafault all python class implicitly inherit from object base class\n",
    "class A(object):\n",
    "    def __init__(self):\n",
    "        self.a = \"A\"\n",
    "        \n",
    "    def printMe(self):\n",
    "        print(\"A's printMe called!\")\n",
    "        print('a = {}'.format(self.a))\n",
    "    \n",
    "    def sayHi(self):\n",
    "        print('{} says HI!'.format(self.a))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 117,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
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     "text": [
      "A's printMe called!\n",
      "a = A\n",
      "A says HI!\n"
     ]
    }
   ],
   "source": [
    "obja = A()\n",
    "obja.printMe()\n",
    "obja.sayHi()"
   ]
  },
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   "cell_type": "code",
   "execution_count": 118,
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   "source": [
    "# single inheritance\n",
    "class B(A):\n",
    "    def __init__(self):\n",
    "        # must explictly invoke base classes constructors\n",
    "        # to inherit properties/attributes\n",
    "        A.__init__(self) # try commenting this out\n",
    "        self.b = 'B'\n",
    "\n",
    "    def update(self):\n",
    "        print(\"Attributes before modifaction: {} and {}\".format(self.a, self.b))\n",
    "        self.a = 'AAA' #can modify inherited attributes\n",
    "        print(\"Attributes after modification: {} and {}\".format(self.a, self.b))\n",
    "        \n",
    "    # overrides inherited printMe\n",
    "    def printMe(self):\n",
    "        print(\"B's printMe called\")\n",
    "        print('a = {}'.format(self.a))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 119,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Attributes before modifaction: A and B\n",
      "Attributes after modification: AAA and B\n"
     ]
    }
   ],
   "source": [
    "objb = B()\n",
    "# shows that A's properties are inherited by B\n",
    "objb.update()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 121,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "obja's property a = A\n",
      "objb's property a = AAA\n"
     ]
    }
   ],
   "source": [
    "# object a's properties are independent from object b's properties\n",
    "print(\"obja's property a = {}\".format(obja.a))\n",
    "print(\"objb's property a = {}\".format(objb.a))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 122,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "AAA says HI!\n"
     ]
    }
   ],
   "source": [
    "# B inherits A's sayHi()\n",
    "# what is the output of the following?\n",
    "objb.sayHi()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Overriding\n",
    "- child class can redefine method that are inherited from parent class with the same name\n",
    "- e.g., printMe() method in class B overrides A's printMe\n",
    "- A's printme can still be called \n",
    "    - syntax\n",
    "    ```\n",
    "    ClassName.method(object)\n",
    "    ```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 123,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "B's printMe called\n",
      "a = AAA\n"
     ]
    }
   ],
   "source": [
    "objb.printMe()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 124,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "A's printMe called!\n",
      "a = A\n"
     ]
    }
   ],
   "source": [
    "A.printMe(obja)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 125,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "A's printMe called!\n",
      "a = AAA\n"
     ]
    }
   ],
   "source": [
    "A.printMe(objb)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 130,
   "metadata": {},
   "outputs": [],
   "source": [
    "# C inherits from B which inherits from A\n",
    "class C(B):\n",
    "    def __init__(self):\n",
    "        B.__init__(self)\n",
    "        self.c = 'C'\n",
    "    \n",
    "    def printMe(self):\n",
    "        print(\"C's printMe called:\")\n",
    "        print(\"Attributes are {}, {}, {}\".format(self.c, self.b, self.a))\n",
    "        "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 131,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "C's printMe called:\n",
      "Attributes are C, B, A\n"
     ]
    }
   ],
   "source": [
    "c1 = C()\n",
    "c1.printMe()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 132,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "A says HI!\n"
     ]
    }
   ],
   "source": [
    "# sayHi() inherited from A\n",
    "c1.sayHi()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 129,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Attributes before modifaction: A and B\n",
      "Attributes after modification: AAA and B\n"
     ]
    }
   ],
   "source": [
    "c1.update()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Multiple Inheritance\n",
    "- Python allows a class to derive/inherit from multiple base classes\n",
    "    - similar to C++\n",
    "- Java doesn't allow it (it's messy!)\n",
    "<img src=\"resources/MultipleInheritance.png\" width=\"75%\">"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 153,
   "metadata": {},
   "outputs": [],
   "source": [
    "# not required to explictly inherit from object class\n",
    "class D:\n",
    "    def __init__(self):\n",
    "        self.a = 'AAAAA'\n",
    "        self.d = 'D'\n",
    "        \n",
    "    def scream(self):\n",
    "        print(\"D's scream() called:\")\n",
    "    \n",
    "# class E inherits from class C and D\n",
    "class E(C, D):\n",
    "    def __init__(self):\n",
    "        # the order in which the base constructors are called matters!\n",
    "        # same attributes of proior constructors are overridden by later constructors\n",
    "        # e.g., try switching D and C's construntor calls\n",
    "        D.__init__(self)\n",
    "        C.__init__(self)\n",
    "        self.e = 'E'\n",
    "    \n",
    "    def printMe(self):\n",
    "        print(\"E's printMe called:\")\n",
    "        print(\"Attributes are {}, {}, {}, {}, {}\".format(self.e, self.d, self.c, self.b, self.a))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 154,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "E's printMe called:\n",
      "Attributes are E, D, C, B, A\n"
     ]
    }
   ],
   "source": [
    "e1 = E()\n",
    "e1.printMe()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 155,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "D's scream() called:\n"
     ]
    }
   ],
   "source": [
    "e1.scream()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 156,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "A says HI!\n"
     ]
    }
   ],
   "source": [
    "e1.sayHi()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## abc module - Abstract Base Classes\n",
    "- allows to define ABCs with abstract methods @abstractmethod decorators"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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