docs/examples/notebooks/Capturing Output.ipynb

{
 "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": []
    }
   ]
  }
 ]
}