16. Iterator & Generator.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Iterators\n",
    "\n",
    "An iterator can be seen as a pointer to a container, e.g. a list structure that can iterate over all the elements of this container. The iterator is an abstraction, which enables the programmer to access all the elements of a container (a set, a list and so on) without any deeper knowledge of the data structure of this container object. In some object oriented programming languages, like Perl, Java and Python, iterators are implicitly available and can be used in foreach loops, corresponding to for loops in Python.\n",
    "\n",
    "Generators are a special kind of function, which enable us to implement or generate iterators.\n",
    "\n",
    "Iterators are a fundamental concept of Python.\n",
    "Mostly, iterators are implicitly used, like in the for-loop of Python. We demonstrate this in the following example. We are iterating over a list, but you shouldn't be mistaken: A list is not an iterator, but it can be used like an iterator:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one\n",
      "two\n",
      "three\n",
      "four\n"
     ]
    }
   ],
   "source": [
    "l = ['one','two','three','four']\n",
    "for i in l:\n",
    "    print(i)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "What is really happening, when you use an iterable like a string, a list, or a tuple, inside of a for loop is the following: The function \"iter\" is called on the iterable. The return value of iter is an iterable. We can iterate over this iterable with the next function until the iterable is exhausted and returns a StopIteration exception:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one\n",
      "two\n",
      "three\n",
      "four\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-20-42d26178ae8a>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      4\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0ml_iterator\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      5\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0ml_iterator\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 6\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0ml_iterator\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "l_iterator = iter(l)\n",
    "print(next(l_iterator))\n",
    "print(next(l_iterator))\n",
    "print(next(l_iterator))\n",
    "print(next(l_iterator))\n",
    "print(next(l_iterator))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Internally, the for loop also calls the next function and terminates, when it gets StopIteration.\n",
    "\n",
    "We can simulate this iteration behavior of the for loop in a while loop: You might have noticed that there is something missing in our program: We have to catch the \"Stop Iteration\" exception:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one\n",
      "two\n",
      "three\n",
      "four\n"
     ]
    }
   ],
   "source": [
    "l_iterator = iter(l)\n",
    "while l_iterator:\n",
    "    try:\n",
    "        print(next(l_iterator))\n",
    "    except StopIteration:\n",
    "        break"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The sequential base types as well as the majority of the classes of the standard library of Python support iteration. The dictionary data type dict supports iterators as well. In this case the iteration runs over the keys of the dictionary:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "The capital city of France is Paris\n",
      "The capital city of Netherlands is Amsterdam\n",
      "The capital city of Germany is Berlin\n",
      "The capital city of Switzerland is Bern\n",
      "The capital city of Austria is Vienna\n"
     ]
    }
   ],
   "source": [
    "capitals = { \"France\"    :\"Paris\", \n",
    "            \"Netherlands\":\"Amsterdam\", \n",
    "            \"Germany\"    :\"Berlin\", \n",
    "            \"Switzerland\":\"Bern\", \n",
    "            \"Austria\"    :\"Vienna\"}\n",
    "for country in capitals:\n",
    "    print(\"The capital city of \" + country + \" is \" + capitals[country])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Generators\n",
    "\n",
    "On the surface generators in Python look like functions, but there is both a syntactic and a semantic difference. One distinguishing characteristic is the yield statements. The yield statement turns a functions into a generator. A generator is a function which returns a generator object. This generator object can be seen like a function which produces a sequence of results instead of a single object. This sequence of values is produced by iterating over it, e.g. with a for loop. The values, on which can be iterated, are created by using the yield statement. The value created by the yield statement is the value following the yield keyword. The execution of the code stops when a yield statement has been reached. The value behind the yield will be returned. The execution of the generator is interrupted now. As soon as \"next\" is called again on the generator object, the generator function will resume execution right after the yield statement in the code, where the last call exited. The execution will continue in the state in which the generator was left after the last yield. This means that all the local variables still exists, because they are automatically saved between calls. This is a fundamental difference to functions: functions always start their execution at the beginning of the function body, regardless where they had left in previous calls. They don't have any static or persistent values. There may be more than one yield statement in the code of a generator or the yield statement might be inside the body of a loop. If there is a return statement in the code of a generator, the execution will stop with a StopIteration exception error if this code is executed by the Python interpreter. The word \"generator\" is sometimes ambiguously used to mean both the generator function itself and the objects which are generated by a generator.\n",
    "\n",
    "Everything which can be done with a generator can also be implemented with a class based iterator as well. But the crucial advantage of generators consists in automatically creating the methods ```__iter__() & next().```\n",
    "\n",
    "##### Generators provide a very neat way of producing data which is huge or infinite."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 80,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "London\n",
      "Hamburg\n",
      "Konstanz\n",
      "Amsterdam\n",
      "Berlin\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-80-063a5502297a>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     16\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mcity\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     17\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mcity\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 18\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mcity\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "# this generator capable to producing of various city names\n",
    "\n",
    "def city_generator():\n",
    "    yield (\"London\")\n",
    "    yield (\"Hamburg\")\n",
    "    yield (\"Konstanz\")\n",
    "    yield (\"Amsterdam\")\n",
    "    yield (\"Berlin\")\n",
    "\n",
    "\n",
    "# It's possible to create a generator object with this generator, which generates all the city names, one after the other:\n",
    "city = city_generator()\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 81,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "London\n",
      "Hamburg\n",
      "Konstanz\n",
      "Amsterdam\n",
      "Berlin\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "I'm in luv with that adorable girl",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-81-f129b9d08947>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     16\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mcity\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     17\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mcity\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 18\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mcity\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m: I'm in luv with that adorable girl"
     ]
    }
   ],
   "source": [
    "# this generator capable to producing of various city names\n",
    "\n",
    "def city_generator():\n",
    "    yield (\"London\")\n",
    "    yield (\"Hamburg\")\n",
    "    yield (\"Konstanz\")\n",
    "    yield (\"Amsterdam\")\n",
    "    yield (\"Berlin\")\n",
    "    return \"I'm in luv with that adorable girl\"\n",
    "\n",
    "# It's possible to create a generator object with this generator, which generates all the city names, one after the other:\n",
    "city = city_generator()\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n",
    "print(next(city))\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Can you see the difference?\n",
    "\n",
    "Since Python 3.3, generators can also use return statements, but a generator still needs at least one yield statement to be a generator! A return statement inside of a generator is equivalent to raise StopIteration()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Can we send a reset to an iterator is a frequently asked question, so that it can start the iteration all over again. There is no reset, but it's possible to create another generator. This can be done e.g. by having the statement \"x = city_generator()\" again."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## using a \"return\" in a generator"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 87,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n"
     ]
    },
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "C:\\Users\\GirrajJangid\\Anaconda3\\lib\\site-packages\\ipykernel_launcher.py:9: DeprecationWarning: generator 'gen' raised StopIteration\n",
      "  if __name__ == '__main__':\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "42",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-87-dee2390da2df>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      7\u001b[0m \u001b[0mg\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mgen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      8\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 9\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;32m<ipython-input-87-dee2390da2df>\u001b[0m in \u001b[0;36mgen\u001b[1;34m()\u001b[0m\n\u001b[0;32m      3\u001b[0m \u001b[1;32mdef\u001b[0m \u001b[0mgen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      4\u001b[0m     \u001b[1;32myield\u001b[0m \u001b[1;36m1\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 5\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m42\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      6\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      7\u001b[0m \u001b[0mg\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mgen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mStopIteration\u001b[0m: 42"
     ]
    }
   ],
   "source": [
    "# next always run the statement which written after yield, here exception written so it raise that exception\n",
    "\n",
    "def gen():\n",
    "    yield 1\n",
    "    raise StopIteration(42)\n",
    "\n",
    "g = gen()\n",
    "print(next(g))\n",
    "print(next(g))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 90,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "42",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-90-817e40ecd87a>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      7\u001b[0m \u001b[0mg\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mgen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      8\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 9\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m: 42"
     ]
    }
   ],
   "source": [
    "# We demonstrate now that return is equivalent, or \"nearly\", if we disregard one line of the traceback:\n",
    "\n",
    "def gen():\n",
    "    yield 1\n",
    "    return 42\n",
    "\n",
    "g = gen()\n",
    "print(next(g))\n",
    "print(next(g))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# send Method / Coroutines"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Generators can not only send objects but also receive objects. Sending a message, i.e. an object, into the generator can be achieved by applying the send method to the generator object. Be aware of the fact that send both sends a value to the generator and returns the value yielded by the generator. We will demonstrate this behavior in the following simple example of a coroutine:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 100,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<generator object simple_coroutine at 0x0000017AE38020A0>"
      ]
     },
     "execution_count": 100,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def simple_coroutine():\n",
    "    print(\"coroutine has been started!\")\n",
    "    x = yield \n",
    "    print(\"coroutine received: \", x)\n",
    "\n",
    "cr = simple_coroutine()\n",
    "cr "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 101,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "coroutine has been started!\n"
     ]
    }
   ],
   "source": [
    "next(cr)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 102,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "coroutine received:  Hi\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-102-d397353bc8ab>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mcr\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0msend\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Hi\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "cr.send(\"Hi\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "To use the send method the generator has to wait at a yield statement, so that the data sent can be processed or assigned to the variable on the left side. What we haven't said so far: A next call also sends and receives. It always sends a None object. The values sent by \"next\" and \"send\" are assigned to a variable within the generator: this variable is called \"message\" in the following example. We called the generator infinit_looper, because it takes a sequential data objects and creates an iterator, which is capable of looping forever over the object, i.e. it starts again with the first element after having delivered the last object. By sending an index to the iterator, we can continue at an arbitrary position."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 167,
   "metadata": {},
   "outputs": [],
   "source": [
    "def infinite_looper(string):\n",
    "    count = 0\n",
    "    while True:\n",
    "        if count >= len(string):\n",
    "            count = 0\n",
    "        message = yield string[count] # yield return objects[count] and receieved message assign to the message variable\n",
    "        if message != None:           # this condition will true if you send any messsage\n",
    "            count = 0 if message < 0 else message # assign count = message on condition\n",
    "        else:\n",
    "            count += 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 150,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "A\n",
      " \n",
      "s\n",
      "t\n"
     ]
    }
   ],
   "source": [
    "x = infinite_looper(\"A string with some words\")\n",
    "print(next(x))\n",
    "print(next(x))\n",
    "print(next(x))\n",
    "print(next(x))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 151,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "s\n",
      "t\n"
     ]
    }
   ],
   "source": [
    "print(x.send(2))\n",
    "print(x.send(3))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# the Throw method"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The throw() method raises an exception at the point where the generator was paused, and returns the next value yielded by the generator. It raises StopIteration if the generator exits without yielding another value. The generator has to catch the passed-in exception, otherwise the exception will be propagated to the caller. The infinite_looper from our previous example keeps yielding the elements of the sequential data, but we don't have any information about the index or the state of the variable \"count\". We can get this information by throwing an exception with the \"throw\" method. We catch this exception inside of the generator and print the value of \"count\":"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 152,
   "metadata": {},
   "outputs": [],
   "source": [
    "def infinite_looper(objects):\n",
    "    count = 0\n",
    "    while True:\n",
    "        if count >= len(objects):\n",
    "            count = 0\n",
    "        try:\n",
    "            message = yield objects[count]\n",
    "        except Exception:\n",
    "            print(\"index: \" + str(count))\n",
    "        if message != None:\n",
    "            count = 0 if message < 0 else message\n",
    "        else:\n",
    "            count += 1\n",
    "            "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 156,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "P\n",
      "y\n"
     ]
    }
   ],
   "source": [
    "looper = infinite_looper(\"Python\")\n",
    "print(next(looper))\n",
    "print(next(looper))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 157,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "index: 1\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "'t'"
      ]
     },
     "execution_count": 157,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "looper.throw(Exception)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 158,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'h'"
      ]
     },
     "execution_count": 158,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(looper)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 159,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'y'"
      ]
     },
     "execution_count": 159,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "looper.send(1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Decorating Generators\n",
    "\n",
    "There is one problem with our approach, we cannot start the iterator by sending directly an index to it. Before we can do this, we need to use the next function to start the iterator and advance it to the yield statement. We will write a decorator now, which can be used to make a decorator ready, by advancing it automatically at creation time to the yield statement. This way, it will be possible to use the send method directly after initialisation of a generator object."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 169,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "can't send non-None value to a just-started generator",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-169-c495eb3c1c4d>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     11\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     12\u001b[0m \u001b[0mx\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0minfinite_looper\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"A string with some words\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 13\u001b[1;33m \u001b[0mx\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0msend\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m2\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: can't send non-None value to a just-started generator"
     ]
    }
   ],
   "source": [
    "def infinite_looper(string):\n",
    "    count = 0\n",
    "    while True:\n",
    "        if count >= len(string):\n",
    "            count = 0\n",
    "        message = yield string[count] # yield return objects[count] and receieved message assign to the message variable\n",
    "        if message != None:           # this condition will true if you send any messsage\n",
    "            count = 0 if message < 0 else message # assign count = message on condition\n",
    "        else:\n",
    "            count += 1\n",
    "            \n",
    "x = infinite_looper(\"A string with some words\")\n",
    "x.send(2)  # we need first initialize iterator and make function to reach yield statement then only send will work"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 170,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a\n",
      "e\n",
      "f\n",
      "a\n",
      "f\n",
      "a\n"
     ]
    }
   ],
   "source": [
    "from functools import wraps\n",
    "\n",
    "def get_ready(gen):\n",
    "    \"\"\"\n",
    "    Decorator: gets a generator gen ready \n",
    "    by advancing to first yield statement\n",
    "    \"\"\"\n",
    "    @wraps(gen)   # euqivalent to generator = wraps(generator)\n",
    "    def generator(*args,**kwargs):   \n",
    "        g = gen(*args,**kwargs)   \n",
    "        next(g)   \n",
    "        return g   \n",
    "    return generator\n",
    "\n",
    "\n",
    "@get_ready\n",
    "def infinite_looper(objects):\n",
    "    count = -1\n",
    "    message = yield None\n",
    "    while True:\n",
    "        count += 1\n",
    "        if message != None:\n",
    "            count = 0 if message < 0 else message\n",
    "        if count >= len(objects):\n",
    "            count = 0\n",
    "        message = yield objects[count]\n",
    "            \n",
    "\n",
    "x = infinite_looper(\"abcdef\") \n",
    "print(next(x))\n",
    "print(x.send(4))\n",
    "print(next(x))\n",
    "print(next(x))\n",
    "print(x.send(5))\n",
    "print(next(x))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# yield from"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`\"yield from\"` is available since Python 3.3!\n",
    "\n",
    "The yield from <expr> statement can be used inside the body of a generator. <expr> has to be an expression evaluating to an iterable, from which an iterator will be extracted.\n",
    "The iterator is run to exhaustion, i.e. until it encounters a StopIteration exception. This iterator yields and receives values to or from the caller of the generator, i.e. the one which contains the yield from statement.\n",
    "\n",
    "We can learn from the following example by looking at the two generators 'gen1' and 'gen2' that yield from is substituting the for loops of 'gen1':\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 171,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "g1: , P, y, t, h, o, n, 0, 1, 2, 3, 4, \n",
      "g2: , P, y, t, h, o, n, 0, 1, 2, 3, 4, \n"
     ]
    }
   ],
   "source": [
    "def gen1():\n",
    "    for char in \"Python\":\n",
    "        yield char\n",
    "    for i in range(5):\n",
    "        yield i\n",
    "\n",
    "def gen2():\n",
    "    yield from \"Python\" # Generator into Generator\n",
    "    yield from range(5)\n",
    "\n",
    "    \n",
    "g1 = gen1()\n",
    "g2 = gen2()\n",
    "print(\"g1: \", end=\", \")\n",
    "for x in g1: # for loop automatical detect StopIteration exception and stop the iteration that's why it stop printing after sometime\n",
    "    print(x, end=\", \")\n",
    "print(\"\\ng2: \", end=\", \")\n",
    "for x in g2:\n",
    "    print(x, end=\", \")\n",
    "print()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The benefit of a yield from statement can be seen as a way to split a generator into multiple generators. That's what we have done in our previous example and we will demonstrate this more explicitely in the following example:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 172,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "True\n"
     ]
    }
   ],
   "source": [
    "def cities():\n",
    "    for city in [\"Berlin\", \"Hamburg\", \"Munich\", \"Freiburg\"]:\n",
    "        yield city\n",
    "\n",
    "def squares():\n",
    "    for number in range(10):\n",
    "        yield number ** 2\n",
    "        \n",
    "        \n",
    "def generator_all_in_one():\n",
    "    for city in cities():\n",
    "        yield city\n",
    "    for number in squares():\n",
    "        yield number\n",
    "        \n",
    "def generator_splitted():\n",
    "    yield from cities()\n",
    "    yield from squares()\n",
    "    \n",
    "lst1 = [el for el in generator_all_in_one()]\n",
    "lst2 = [el for el in generator_splitted()]\n",
    "print(lst1 == lst2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 176,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['Berlin', 'Hamburg', 'Munich', 'Freiburg', 0, 1, 4, 9, 16, 25, 36, 49, 64, 81]\n",
      "['Berlin', 'Hamburg', 'Munich', 'Freiburg', 0, 1, 4, 9, 16, 25, 36, 49, 64, 81]\n"
     ]
    }
   ],
   "source": [
    "print(lst1)\n",
    "print(lst2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The previous code returns True because the generators generator_all_in_one and generator_splitted yield the same elements. This means that if the <expr> from the yield from is another generator, the effect is the same as if the body of the sub‐generator were inlined at the point of the yield from statement. Furthermore, the subgenerator is allowed to execute a return statement with a value, and that value becomes the value of the yield from expression. We demonstrate this with the following little script:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 177,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "42\n"
     ]
    }
   ],
   "source": [
    "def subgenerator():\n",
    "    yield 1\n",
    "    return 42\n",
    "\n",
    "def delegating_generator():\n",
    "    x = yield from subgenerator()\n",
    "    print(x)\n",
    "\n",
    "for x in delegating_generator():\n",
    "    print(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The full semantics of the yield from expression is described in six points in \"PEP 380 -- Syntax for Delegating to a Subgenerator\" in terms of the generator protocol:\n",
    "1. Any values that the iterator yields are passed directly to the caller.\n",
    "2. Any values sent to the delegating generator using `send()` are passed directly to the iterator. If the sent value is `None`, the iterator's `__next__()` method is called. If the sent value is not None, the iterator's `send()` method is called. If the call raises `StopIteration`, the delegating generator is resumed. Any other exception is propagated to the delegating generator.\n",
    "3. Exceptions other than GeneratorExit thrown into the delegating generator are passed to the `throw()` method of the iterator. If the call raises `StopIteration`, the delegating generator is resumed. Any other exception is propagated to the delegating generator.\n",
    "4. If a GeneratorExit exception is thrown into the delegating generator, or the `close()` method of the delegating generator is called, then the `close()` method of the iterator is called if it has one. If this call results in an exception, it is propagated to the delegating generator. Otherwise, GeneratorExit is raised in the delegating generator.\n",
    "5. The value of the `yield from` expression is the first argument to the StopIteration exception raised by the iterator when it terminates.\n",
    "6. `return expr` in a generator causes `StopIteration(expr)` to be raised upon exit from the generator."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 185,
   "metadata": {},
   "outputs": [],
   "source": [
    "class even:\n",
    "    def __init__(self,start,max_limit):                             # iter contain 3 values new val ,old ,value ,counter\n",
    "        if start % 2 == 0 :\n",
    "            self.start = start\n",
    "        else:\n",
    "            self.start = start + 1\n",
    "        self.max_limit = max_limit\n",
    "    \n",
    "    def __iter__(self):\n",
    "        self.val = self.start\n",
    "        return self\n",
    "    \n",
    "    def __next__(self):\n",
    "        if self.val <= self.max_limit:\n",
    "            self.val += 2\n",
    "            return self.val\n",
    "        else:\n",
    "            raise StopIteration('Max limit has executed')\n",
    "\n",
    "obj = even(1,10000000)\n",
    "# create obj to iterator\n",
    "obj = iter(obj)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 186,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "4"
      ]
     },
     "execution_count": 186,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(obj)    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 187,
   "metadata": {},
   "outputs": [],
   "source": [
    "from math import sqrt\n",
    "class prime:\n",
    "    def __init__(self,start,max_limit):\n",
    "        self.start = start\n",
    "        self.max_limit = max_limit\n",
    "    def __iter__(self):\n",
    "        self.val = self.start\n",
    "        return self\n",
    "    def __next__(self):\n",
    "        if self.val <= self.max_limit:\n",
    "            for i in range(2,round(sqrt(self.val)+1)):\n",
    "                if self.val % i == 0:\n",
    "                    pass\n",
    "                else :\n",
    "                    self.val = i\n",
    "                self.start = start\n",
    "                self.val = self.prime\n",
    "            return self.val\n",
    "        else:\n",
    "            raise StopIteration('Max limit has executed')\n",
    "\n",
    "obj = prime(1,1000)\n",
    "# create obj to iterator\n",
    "obj = iter(obj)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 188,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 188,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(obj)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 189,
   "metadata": {},
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "unexpected EOF while parsing (<ipython-input-189-0db7594d79d1>, line 23)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-189-0db7594d79d1>\"\u001b[1;36m, line \u001b[1;32m23\u001b[0m\n\u001b[1;33m    \u001b[0m\n\u001b[1;37m    ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m unexpected EOF while parsing\n"
     ]
    }
   ],
   "source": [
    "# generators\n",
    "def even(num,max):\n",
    "    c = 0\n",
    "    while c<= max:\n",
    "        if num % 2 == 0:\n",
    "            yield True \n",
    "            #num\n",
    "            num += 1\n",
    "            c += 1\n",
    "            print('one ', c)\n",
    "        else:\n",
    "            num +=1\n",
    "            c += 1\n",
    "            print('two', c)\n",
    "\n",
    "x=even(2,20)\n",
    "def prime(maxx):\n",
    "    c = 2\n",
    "    while c<maxx:\n",
    "        if maxx%c==0:\n",
    "            \n",
    "\n",
    "    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 190,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "'int' object is not an iterator",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-190-92de4e9f6b1e>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mx\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: 'int' object is not an iterator"
     ]
    }
   ],
   "source": [
    "next(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 191,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{3, 5, 7, 9, 11, 13, 15, 17, 19}\n"
     ]
    }
   ],
   "source": [
    "def prime(n):\n",
    "    l = []\n",
    "    if n==1:\n",
    "        return 1\n",
    "    elif n>1:\n",
    "        for i in range(2,n):\n",
    "            for j in range(2,i):\n",
    "                if i%j==0:\n",
    "                    break\n",
    "                else :\n",
    "                    \n",
    "                    l.append(i)\n",
    "    l = set(l)\n",
    "    return l\n",
    "print(prime(20))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "# Iterator Example"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 192,
   "metadata": {},
   "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",
      "10\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-192-47e7bfb934e8>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     14\u001b[0m \u001b[0mh\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0miter\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mh\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     15\u001b[0m \u001b[1;32mwhile\u001b[0m \u001b[1;32mTrue\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 16\u001b[1;33m         \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mh\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;32m<ipython-input-192-47e7bfb934e8>\u001b[0m in \u001b[0;36m__next__\u001b[1;34m(self)\u001b[0m\n\u001b[0;32m     10\u001b[0m             \u001b[1;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mn\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     11\u001b[0m         \u001b[1;32melse\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 12\u001b[1;33m             \u001b[1;32mraise\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     13\u001b[0m \u001b[0mh\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mhello\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m10\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     14\u001b[0m \u001b[0mh\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0miter\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mh\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "class hello:\n",
    "    def __init__(self , maxi = 0):\n",
    "        self.maxi = maxi\n",
    "    def __iter__(self):\n",
    "        self.n = 0\n",
    "        return self\n",
    "    def __next__(self):\n",
    "        if self.n <self.maxi:\n",
    "            self.n += 1\n",
    "            return self.n\n",
    "        else:\n",
    "            raise StopIteration\n",
    "h = hello(10)\n",
    "h = iter(h)\n",
    "while True:\n",
    "        print(next(h))  "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 193,
   "metadata": {},
   "outputs": [],
   "source": [
    "h = hello(100)\n",
    "h = iter(h)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 194,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , "
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-194-89c827cc4196>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;32mwhile\u001b[0m \u001b[1;32mTrue\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mh\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mend\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m\" , \"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;32m<ipython-input-192-47e7bfb934e8>\u001b[0m in \u001b[0;36m__next__\u001b[1;34m(self)\u001b[0m\n\u001b[0;32m     10\u001b[0m             \u001b[1;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mn\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     11\u001b[0m         \u001b[1;32melse\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 12\u001b[1;33m             \u001b[1;32mraise\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     13\u001b[0m \u001b[0mh\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mhello\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m10\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     14\u001b[0m \u001b[0mh\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0miter\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mh\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "while True:\n",
    "    print(next(h),end = \" , \")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 195,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "3\n",
      "5\n",
      "7\n",
      "9\n",
      "11\n",
      "13\n",
      "15\n",
      "17\n",
      "19\n"
     ]
    },
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-195-67eb788093ba>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     18\u001b[0m \u001b[0mf\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0miter\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mf\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     19\u001b[0m \u001b[1;32mwhile\u001b[0m \u001b[1;32mTrue\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 20\u001b[1;33m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mf\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;32m<ipython-input-195-67eb788093ba>\u001b[0m in \u001b[0;36m__next__\u001b[1;34m(self)\u001b[0m\n\u001b[0;32m     14\u001b[0m             \u001b[1;32mreturn\u001b[0m \u001b[0mv\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     15\u001b[0m         \u001b[1;32melse\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 16\u001b[1;33m             \u001b[1;32mraise\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     17\u001b[0m \u001b[0mf\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mOddNumber\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m10\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     18\u001b[0m \u001b[0mf\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0miter\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mf\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "# First N odd Numbers\n",
    "class OddNumber:\n",
    "    def __init__(self,maxi = 0):\n",
    "        self.maxi = maxi\n",
    "        self.c = 1\n",
    "    def __iter__(self):\n",
    "        self.n = 1\n",
    "        return self\n",
    "    def __next__(self):\n",
    "        v = self.n\n",
    "        if self.c <= self.maxi:\n",
    "            self.c +=1\n",
    "            self.n +=2\n",
    "            return v\n",
    "        else:\n",
    "            raise StopIteration\n",
    "f = OddNumber(10)\n",
    "f = iter(f)\n",
    "while True:\n",
    "    print(next(f))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# INFINITE LOOP without storing anything into a RAM\n",
    "\n",
    "import time\n",
    "def mygen():\n",
    "    x = 0\n",
    "    while True :\n",
    "        x = x + 1\n",
    "        yield print(\"Hello World {} Times\".format(x))\n",
    "\n",
    "v = mygen()\n",
    "while True :\n",
    "    next(v)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Generator"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "k = (i**2 for i in range(100) if i % 2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "next(k)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 98,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Genter Successfully Exited\n",
      "I will execute no matter whatever happens\n"
     ]
    }
   ],
   "source": [
    "while True :\n",
    "    try :\n",
    "        print(next(k),end='\\t')\n",
    "    except StopIteration as e :\n",
    "        print(\"Genter Successfully Exited\")\n",
    "        break\n",
    "    else : # execute when no exception raise\n",
    "        print(\"Something is happening\")\n",
    "    finally :\n",
    "        print(\"I will execute no matter whatever happens\")\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 128,
   "metadata": {},
   "outputs": [],
   "source": [
    "def gen(n,p):\n",
    "    c = 1\n",
    "    while c <= p :\n",
    "        yield n**c\n",
    "        c = c + 1\n",
    "k = gen(2 ,  5 )  # 2 ki power 5 tak\n",
    "#k = gen(int(input(\"Enter a Number : \")),int(input(\"Enter max. Power : \")))\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 134,
   "metadata": {},
   "outputs": [
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-134-46b1c9a820bb>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mnext\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mk\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "next(k)"
   ]
  }
 ],
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