A Gentle Introduction to Python Part 2.ipynb

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   "metadata": {},
   "source": [
    "# A Gentle Introduction to Python Part 2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Assumes that you already set up jupyter successfully. Assumes that you have had exposure to an object-oriented programming language like Java or C++ before. Assumes that you are familar with the concepts presented in [Part 1](https://github.com/BigDataAnalyticsGroup/bigdataengineering/blob/master/A%20Gentle%20Introduction%20to%20Python.ipynb)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Copyright Jens Dittrich, [Big Data Analytics Group](https://bigdata.uni-saarland.de/), [CC-BY-SA](https://creativecommons.org/licenses/by-sa/4.0/legalcode)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Python: Comprehensions and Functional Programming"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "A standard for-loop:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0\n",
      "1\n",
      "2\n",
      "3\n",
      "4\n"
     ]
    }
   ],
   "source": [
    "# Syntax:\n",
    "# for item in list:\n",
    "#    expression\n",
    "for n in range(5):\n",
    "    print(n)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**vs** a list comprehension:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4]"
      ]
     },
     "execution_count": 2,
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     "output_type": "execute_result"
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   ],
   "source": [
    "# Syntax:\n",
    "# [expression for item in list]\n",
    "#    \n",
    "[i for i in range(5)]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "A standard for-loop with an if-clause:"
   ]
  },
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   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0  is even\n",
      "2  is even\n",
      "4  is even\n"
     ]
    }
   ],
   "source": [
    "# Syntax:\n",
    "# for item in list:\n",
    "#    if condition:\n",
    "#        expression\n",
    "for n in range(5):\n",
    "    if n%2 == 0:\n",
    "        print(n, \" is even\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**vs** a list comprehension with an if-clause:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 2, 4]"
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     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "# Syntax:\n",
    "# [expression for item in list if condition]\n",
    "#    \n",
    "ar = [i for i in range(5) if i%2 == 0]\n",
    "ar"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "PS: obviously if the if-clause is just about odd/even numbers or jumping over integer numbers with a fixed offset, we could do this much easier:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 2, 4]"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "[i for i in range(0,5,2)]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4]"
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     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Syntax:\n",
    "# range(start_including [, end_excluding [, stepsize]])\n",
    "list(range(0,5))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 2, 4]"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "ar"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### map"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "map using a named function to map items:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 4, 16]"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def multiply(x):\n",
    "    return (x**2)\n",
    "\n",
    "squared = list(map(multiply, ar))\n",
    "squared"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "map using a lambda-function to map items:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 4, 16]"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "squared2 = list(map(lambda x: x**2, ar))\n",
    "squared2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## unittests"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [],
   "source": [
    "# unittests in Python are very similar to unittests in Java:\n",
    "class Bar:\n",
    "    def __init__(self):\n",
    "        self.a = 42\n",
    "\n",
    "    def whatever(self, par):\n",
    "        if par == 0:\n",
    "            raise ValueError(\"Division by zero is not defined.\")\n",
    "        self.a /= par\n",
    "        return self.a\n",
    "    \n",
    "import unittest\n",
    "\n",
    "class BarTest(unittest.TestCase):\n",
    "\n",
    "    # the following method will be called before every test-Method\n",
    "    def setUp(self):\n",
    "        self.bar = Bar()\n",
    "        \n",
    "    def test_div(self):\n",
    "        self.assertEqual(self.bar.a, 42)\n",
    "        local_a = 42\n",
    "        par = 77\n",
    "        ret = self.bar.whatever(par)\n",
    "        self.assertEqual(ret, local_a/par)\n",
    "        self.assertEqual(self.bar.a, local_a/par)\n",
    "        \n",
    "    def test_init(self):\n",
    "        self.assertEqual(self.bar.a, 42)\n",
    "\n",
    "    def test_divbyzero(self):\n",
    "        with self.assertRaises(ValueError):\n",
    "            self.bar.whatever(0)"
   ]
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   "execution_count": 11,
   "metadata": {},
   "outputs": [
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     "text": [
      "test_div (__main__.BarTest) ... ok\n",
      "test_divbyzero (__main__.BarTest) ... ok\n",
      "test_init (__main__.BarTest) ... ok\n",
      "\n",
      "----------------------------------------------------------------------\n",
      "Ran 3 tests in 0.003s\n",
      "\n",
      "OK\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "<unittest.main.TestProgram at 0x10785ebe0>"
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     "execution_count": 11,
     "metadata": {},
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   "source": [
    "# Run the unit test without shutting down the jupyter kernel\n",
    "unittest.main(argv=['ignored', '-v'], verbosity=2, exit=False)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
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