Short example of closure in Python

closure.ipynb

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      "# prints it's argument, and kwargs.\n",
      "def foo(x, **kwargs):\n",
      "    print 'x: {}'.format(x)\n",
      "    print 'kwargs: {}'.format(kwargs)\n",
      "    \n",
      "\n",
      "# invokes whatever function it is passed\n",
      "# with a fixed argument.\n",
      "def bar(fctn):\n",
      "    # note, I never set kwargs\n",
      "    fctn('from boo!')\n",
      "\n",
      "    \n",
      "# calls bar using the foo function    \n",
      "def bar_calling_foo():\n",
      "    bar(foo)\n",
      "\n",
      "\n",
      "# passes foo with kwargs filled in to bar\n",
      "# who then calls it.\n",
      "def bar_calling_foo_with_kwargs(**kwargs):\n",
      "    \n",
      "    # note that the 'a' here is totally seperate\n",
      "    # to the 'x' above. Although the name is different\n",
      "    # it works just fine - all we care about is the \n",
      "    # position of the arguments.\n",
      "    def foo_closure(a):\n",
      "        # a wrapper, closes over the kwargs\n",
      "        return foo(a, **kwargs)\n",
      "    \n",
      "    # invoke bar, passing our closure.\n",
      "    # foo_closure will still enjoy access to our\n",
      "    # namespace! This is a *closure*.\n",
      "    bar(foo_closure)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
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     "cell_type": "code",
     "collapsed": false,
     "input": [
      "foo('calling foo directly', hello='world')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
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       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "x: calling foo directly\n",
        "kwargs: {'hello': 'world'}\n"
       ]
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "bar(foo)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
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       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "x: from boo!\n",
        "kwargs: {}\n"
       ]
      }
     ],
     "prompt_number": 3
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     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# just putting the above into a function\n",
      "bar_calling_foo()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "x: from boo!\n",
        "kwargs: {}\n"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# now with closure on kwargs\n",
      "bar_calling_foo_with_kwargs(pint='delicious')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "x: from boo!\n",
        "kwargs: {'pint': 'delicious'}\n"
       ]
      }
     ],
     "prompt_number": 5
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