add demo notebook for %%capture

docs/examples/notebooks/Capturing Output.ipynb

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+{
+ "metadata": {
+  "name": "Capturing Output"
+ },
+ "nbformat": 3,
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "heading",
+     "level": 1,
+     "source": [
+      "Capturing Output with <tt>%%capture</tt>"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "source": [
+      "One of IPython's new cell magics is `%%capture`, which captures stdout/err for a cell,",
+      "and discards them or stores them in variables in your namespace."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "import sys"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "markdown",
+     "source": [
+      "By default, it just swallows it up.  This is a simple way to suppress unwanted output."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "%%capture",
+      "print 'hi, stdout'",
+      "print >> sys.stderr, 'hi, stderr'"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "markdown",
+     "source": [
+      "If you specify `-o` or `-e`, then stdout and/or stderr will be stored in those variables in your namespace."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "%%capture -o my_stdout",
+      "print 'hi, stdout'",
+      "print >> sys.stderr, 'hi, stderr'"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "my_stdout"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "%%capture -o my_stdout2 -e my_stderr",
+      "print 'hi again, stdout'",
+      "print >> sys.stderr, 'hi there, stderr'"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "sys.stdout.write(my_stdout2)",
+      "sys.stderr.write(my_stderr)"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "markdown",
+     "source": [
+      "`%%capture` only captures stdout/err, not displaypub, so you can still do plots and use the display protocol inside %%capture"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "%pylab inline"
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "%%capture -o wontshutup",
+      "",
+      "print \"setting up X\"",
+      "x = np.linspace(0,5,1000)",
+      "print \"step 2: constructing y-data\"",
+      "y = np.sin(x)",
+      "print \"step 3: display info about y\"",
+      "plt.plot(x,y)",
+      "print \"okay, I'm done now\""
+     ],
+     "language": "python",
+     "outputs": []
+    },
+    {
+     "cell_type": "code",
+     "input": [
+      "print wontshutup"
+     ],
+     "language": "python",
+     "outputs": []
+    }
+   ]
+  }
+ ]
+}
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