Generator Examples ipython notebook

Generator Examples.ipynb

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      "# Python Generators\n",
      "\n",
      "## What they do\n",
      "\n",
      "* They allow a function to behave as an `Iterator` object.\n",
      "* They can be used to emulate state and concurrency (more on that later)"
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     "input": [
      "\n",
      "def count(a):\n",
      "    \"\"\"counts elements of an iterable\"\"\"\n",
      "    c = 0\n",
      "    for i in a:\n",
      "        c += 1\n",
      "    return c\n",
      "\n",
      "# an array\n",
      "a = range(10)\n",
      "\n",
      "print(count(a))\n",
      "\n",
      "# but what happens as it grows?\n",
      "\n",
      "# a = range(2**16)\n",
      "# a = range(2**32) ??? memory swapping\n",
      "# memory is not Infinite\n",
      "# range creates the whole array in one go. \n",
      "\n",
      "# consider this\n",
      "\n",
      "# Problem: Memory is finite. I want to pretend it's infinite\n",
      "# Solution: create an iterator\n",
      "# iterator is any object that implements __iter__ \n",
      "# and returns an iterable object that implements __next__ or next in py3)\n",
      "\n",
      "\n",
      "class crange(object):\n",
      "    \"\"\"range replacement iterator\"\"\"\n",
      "    def __init__(self, start, end=None, step=1):\n",
      "        if not end:\n",
      "            end = start\n",
      "            start = 0\n",
      "        assert start <= end\n",
      "        self.start = start\n",
      "        self.end = end\n",
      "        self.step = step\n",
      "\n",
      "    def next(self):\n",
      "        if self.start >= self.end:\n",
      "            raise StopIteration()\n",
      "\n",
      "        res = self.start\n",
      "        self.start += self.step\n",
      "        return res\n",
      "\n",
      "    __next__ = next\n",
      "\n",
      "    def __iter__(self):\n",
      "        return self\n",
      "    \n",
      "for i in crange(10):\n",
      "    print(i)\n",
      "\n",
      "\n",
      "# generator expression:\n",
      "a = (i for i in xrange(10))\n",
      "\n",
      "# but c'mon a whole class for a friggin iterator?\n",
      "# Solution 2: Use a Generator function (a function that yields)\n",
      "def irange(start, end=None, step=1):\n",
      "    \"\"\"go from `start` to `end` by `step`\"\"\"\n",
      "    if not end:\n",
      "        start, end = 0, start\n",
      "\n",
      "    while start < end:\n",
      "        yield start\n",
      "        start += step\n",
      "\n",
      "\n",
      "for i in irange(0,10):\n",
      "    print(i)\n",
      "\n",
      "\n",
      "\n",
      "# force generator to run fully by using it in a constructor\n",
      "a = list(irange(0, 10))\n",
      "print(a)\n",
      "\n",
      "\n",
      "def mdict():\n",
      "    yield 'foo', 1\n",
      "    yield 'bar', 2\n",
      "\n",
      "try:\n",
      "    gen = mdict()\n",
      "    print gen.next()\n",
      "    print gen.next()\n",
      "    print gen.next()\n",
      "except StopIteration, se:\n",
      "    print('mdict finished thus StopIteration was raised')\n",
      "\n",
      "    \n",
      "\n"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
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       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "10\n",
        "0\n",
        "1\n",
        "2\n",
        "3\n",
        "4\n",
        "5\n",
        "6\n",
        "7\n",
        "8\n",
        "9\n",
        "0\n",
        "1\n",
        "2\n",
        "3\n",
        "4\n",
        "5\n",
        "6\n",
        "7\n",
        "8\n",
        "9\n",
        "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]\n",
        "('foo', 1)\n",
        "('bar', 2)\n",
        "mdict finished thus StopIteration was raised\n"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Generators and concurrency\n",
      "\n",
      "### Let's revisit `yield` semantics\n",
      "\n",
      "* Can be suspended by the consumer, saving the state with it\n",
      "* It is resumed by the consumer\n",
      "* It can receive values from the consumer and return values to it\n",
      "* It can raise exceptions\n",
      "\n",
      "### Let's revisit Coroutines\n",
      "\n",
      "* Can be suspended by another coroutine or itself, saving the state with it\n",
      "* It is resumed by another coroutine\n",
      "* It can receive values from another coroutine\n",
      "\n",
      "\n"
     ]
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     "cell_type": "code",
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     "input": [
      "print \"Hello\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Hello\n"
       ]
      }
     ],
     "prompt_number": 18
    }
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}

ipython_install.sh

#!/usr/bin/env bash
pip install pyzmq
pip install ipython