generators.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
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   "source": [
    "## Generators\n",
    "---"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "def fib(a=1, b=1):\n",
    "    while True:\n",
    "        yield a; #-------------> give controll back to caller and continues on next()\n",
    "        a, b = b, a + b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "1\n",
      "2\n",
      "3\n",
      "5\n"
     ]
    }
   ],
   "source": [
    "for idx, x in enumerate(fib()):\n",
    "    if idx == 5: break\n",
    "    print(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "def fib_2(a=1, b=1):\n",
    "    rv = []\n",
    "    for _ in range(5):\n",
    "        rv.append(a)   #---------> wait until all iterations\n",
    "        a, b = b, a + b\n",
    "    return rv"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[1, 1, 2, 3, 5]"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "fib_2()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Consider a hypothetical situation you need the call the below 3 functions in order but it is not in your hand to make it possible. We can achieve this with a generator**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [],
   "source": [
    "class SomeClass:\n",
    "    def first_function(self):\n",
    "        return 'the first'\n",
    "\n",
    "    def second_function(self):\n",
    "        return 'the second'\n",
    "    \n",
    "    def third_function(self):\n",
    "        return 'the third'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [],
   "source": [
    "def the_gen():\n",
    "    cls = SomeClass()\n",
    "    yield cls.first_function()\n",
    "    yield cls.second_function()\n",
    "    yield cls.third_function()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "gn = the_gen()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'the first'"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(gn)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'the second'"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(gn)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'the third'"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(gn)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-22-7c1428ea43c1>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mgn\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# StopIteration: no more values to produce\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "next(gn) # StopIteration: no more values to produce"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Explanation\n",
    "\n",
    "```py\n",
    "def the_gen():\n",
    "    cls = SomeClass()\n",
    "    # call functions in order and yield the result\n",
    "    yield cls.first_function()\n",
    "    yield cls.second_function()\n",
    "    yield cls.third_function()\n",
    "```\n",
    "**`next()` always gives the yield value**\n",
    "\n",
    "```py\n",
    "next(gn)\n",
    "next(gn)\n",
    "next(gn)\n",
    "# you can't change the order of calling method\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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