X4-Control-flow.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Control Flow Statements"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## If"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "if some_condition:\n",
    "    \n",
    "    algorithm"
   ]
  },
  {
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello\n"
     ]
    }
   ],
   "source": [
    "x = 12\n",
    "if x >10:\n",
    "    print(\"Hello\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## If-else"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "if some_condition:\n",
    "    \n",
    "    algorithm\n",
    "    \n",
    "else:\n",
    "    \n",
    "    algorithm"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello\n"
     ]
    }
   ],
   "source": [
    "x = 12\n",
    "if x > 10:\n",
    "    print(\"Hello\")\n",
    "else:\n",
    "    print(\"World\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## if-elif"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "if some_condition:\n",
    "    \n",
    "    algorithm\n",
    "\n",
    "elif some_condition:\n",
    "    \n",
    "    algorithm\n",
    "\n",
    "else:\n",
    "    \n",
    "    algorithm"
   ]
  },
  {
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   "execution_count": 3,
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "x<y\n"
     ]
    }
   ],
   "source": [
    "x = 10\n",
    "y = 12\n",
    "if x > y:\n",
    "    print(\"x>y\")\n",
    "elif x < y:\n",
    "    print(\"x<y\")\n",
    "else:\n",
    "    print(\"x=y\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "if statement inside a if statement or if-elif or if-else are called as nested if statements."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
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    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "x<y\n",
      "x=10\n"
     ]
    }
   ],
   "source": [
    "x = 10\n",
    "y = 12\n",
    "if x > y:\n",
    "    print(\"x>y\")\n",
    "elif x < y:\n",
    "    print(\"x<y\")\n",
    "    if x == 10:\n",
    "        print(\"x=10\")\n",
    "    else:\n",
    "        print(\"invalid\")\n",
    "else:\n",
    "    print(\"x=y\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Loops"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### For"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "for variable in something:\n",
    "    \n",
    "    algorithm"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0\n",
      "1\n",
      "2\n",
      "3\n",
      "4\n"
     ]
    }
   ],
   "source": [
    "for i in range(5):\n",
    "    print(i)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In the above example, `i` iterates over the 0,1,2,3,4. Every time it takes each value and executes the algorithm inside the loop. It is also possible to iterate over a nested list illustrated below."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3]\n",
      "[4, 5, 6]\n",
      "[7, 8, 9]\n"
     ]
    }
   ],
   "source": [
    "list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]\n",
    "for list1 in list_of_lists:\n",
    "        print(list1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "A use case of a nested for loop in this case would be,"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "2\n",
      "3\n",
      "4\n",
      "5\n",
      "6\n",
      "7\n",
      "8\n",
      "9\n"
     ]
    }
   ],
   "source": [
    "list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]\n",
    "for list1 in list_of_lists:\n",
    "    for x in list1:\n",
    "        print(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### While"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "while some_condition:\n",
    "    \n",
    "    algorithm"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "4\n",
      "Bye\n"
     ]
    }
   ],
   "source": [
    "i = 1\n",
    "while i < 3:\n",
    "    print(i ** 2)\n",
    "    i = i + 1\n",
    "print('Bye')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Break"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "As the name says. It is used to break out of a loop when a condition becomes true when executing the loop."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false,
    "execution": {
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0\n",
      "1\n",
      "2\n",
      "3\n",
      "4\n",
      "5\n",
      "6\n",
      "7\n"
     ]
    }
   ],
   "source": [
    "for i in range(100):\n",
    "    print(i)\n",
    "    if i >= 7:\n",
    "        break"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Continue"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This continues the rest of the loop. Sometimes when a condition is satisfied there are chances of the loop getting terminated. This can be avoided using continue statement. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
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    "execution": {
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0\n",
      "1\n",
      "2\n",
      "3\n",
      "4\n",
      "The end.\n",
      "The end.\n",
      "The end.\n",
      "The end.\n",
      "The end.\n"
     ]
    }
   ],
   "source": [
    "for i in range(10):\n",
    "    if i > 4:\n",
    "        print(\"The end.\")\n",
    "        continue\n",
    "    elif i < 7:\n",
    "        print(i)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## List Comprehensions"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python makes it simple to generate a required list with a single line of code using list comprehensions. For example If i need to generate multiples of say 27 I write the code using for loop as,"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
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    "jupyter": {
     "outputs_hidden": false
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[27, 54, 81, 108, 135, 162, 189, 216, 243, 270]\n"
     ]
    }
   ],
   "source": [
    "res = []\n",
    "for i in range(1, 11):\n",
    "    x = 27*i\n",
    "    res.append(x)\n",
    "print(res)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Since you are generating another list altogether and that is what is required, List comprehensions is a more efficient way to solve this problem."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
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   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[27, 54, 81, 108, 135, 162, 189, 216, 243, 270]"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "[27*x for x in range(1, 11)]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "That's it!. Only remember to enclose it in square brackets. There is possibility to make list comprehension conditional adding condition to syntax."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
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   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[27, 81, 135, 189, 243, 297, 351, 405, 459, 513]"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "[27*x for x in range(1, 20) if x % 2 == 1]"
   ]
  },
  {
   "cell_type": "raw",
   "metadata": {},
   "source": [
    "List comprehension can use nested loops as well"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
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    "execution": {
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   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['aA', 'aB', 'aC', 'bA', 'bB', 'bC', 'cA', 'cB', 'cC']"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "[j + k for j in 'abc' for k in 'ABC']"
   ]
  }
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