Example of writing a Table object to an ASCII file and reading it back with no loss of metadata

test_asciitable_format.ipynb

{
 "metadata": {
  "name": "test_asciitable_format"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import astropy.io.ascii as ascii\n",
      "from astropy.table import Table, Column"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Make a table with some non-generic data types and meta values\n",
      "a = Column(name='a', data=[1, 2], dtype='uint8', units='m s**2', format='%04d', description='Column a')\n",
      "b = Column(name='b', data=[3, 4], dtype='float16', units='kg', format='%.3f', description='Column b')\n",
      "t = Table([a, b])\n",
      "t.meta['meta1'] = ['a', 1, {'c': 2}]\n",
      "t.meta['meta2'] = 'meta2'\n",
      "t.meta['meta3'] = 'meta3'\n",
      "t['a'].meta['a'] = ['hello', 'world']\n",
      "t['a'].units = 'm s**2'"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "from StringIO import StringIO\n",
      "out = StringIO()\n",
      "ascii.write(t, out, Writer=ascii.AsciiTable, delimiter=',')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Here is the output of write() in the new \"AsciiTable\" format\n",
      "# The table metadata are encoded in pretty-printed JSON.\n",
      "# The first and last lines are just the column names, which makes\n",
      "# it easy for simple CSV-style readers to parse this output, assuming\n",
      "# they use either the first or last commented line to find the column\n",
      "# names.\n",
      "print out.getvalue()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "# a,b\n",
        "# \n",
        "# -*- ASCIITABLE-FORMAT-HEADER-JSON-START -*-\n",
        "# {\n",
        "#     \"table_meta\": {\n",
        "#         \"meta1\": [\n",
        "#             \"a\",\n",
        "#             1,\n",
        "#             {\n",
        "#                 \"c\": 2\n",
        "#             }\n",
        "#         ],\n",
        "#         \"meta2\": \"meta2\",\n",
        "#         \"meta3\": \"meta3\"\n",
        "#     },\n",
        "#     \"cols\": [\n",
        "#         {\n",
        "#             \"name\": \"a\",\n",
        "#             \"units\": \"m s2\",\n",
        "#             \"format\": \"%04d\",\n",
        "#             \"description\": \"Column a\",\n",
        "#             \"dtype\": \"uint8\",\n",
        "#             \"meta\": {\n",
        "#                 \"a\": [\n",
        "#                     \"hello\",\n",
        "#                     \"world\"\n",
        "#                 ]\n",
        "#             }\n",
        "#         },\n",
        "#         {\n",
        "#             \"name\": \"b\",\n",
        "#             \"units\": \"kg\",\n",
        "#             \"format\": \"%.3f\",\n",
        "#             \"description\": \"Column b\",\n",
        "#             \"dtype\": \"float16\",\n",
        "#             \"meta\": {}\n",
        "#         }\n",
        "#     ]\n",
        "# }\n",
        "# -*- ASCIITABLE-FORMAT-HEADER-JSON-STOP -*-\n",
        "# \n",
        "# a,b\n",
        "0001,3.000\n",
        "0002,4.000\n",
        "\n"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Now read the output of the previous write()\n",
      "# \n",
      "t = ascii.read(out.getvalue(), Reader=ascii.AsciiTable)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 5
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Column units\n",
      "print type(t['a'].units)\n",
      "t['a'].units"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "<class 'astropy.units.core.CompositeUnit'>\n"
       ]
      },
      {
       "latex": [
        "$\\mathrm{s^{2}\\ m}$"
       ],
       "output_type": "pyout",
       "prompt_number": 6,
       "text": [
        "Unit(\"m s2\")"
       ]
      }
     ],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Column meta data\n",
      "t['a'].meta"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 7,
       "text": [
        "OrderedDict([('a', ['hello', 'world'])])"
       ]
      }
     ],
     "prompt_number": 7
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Table metadata preserved as an OrderedDict (with correct order)\n",
      "# This probably needs some work, it depends on the json.loads()\n",
      "# object_pairs_hook option, which is only in python 2.7+.\n",
      "# \n",
      "# There is also a hack because JSON turns everything into unicode,\n",
      "# which messes up Numpy.  So right now there is a simple recursive\n",
      "# routine to encode everything as UTF-8.  This needs work.\n",
      "t.meta"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 8,
       "text": [
        "OrderedDict([('meta1', ['a', 1, OrderedDict([('c', 2)])]), ('meta2', 'meta2'), ('meta3', 'meta3')])"
       ]
      }
     ],
     "prompt_number": 8
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "t  # table formatting preserved"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "html": [
        "<table><tr><th>a</th><th>b</th></tr><tr><td>0001</td><td>3.000</td></tr><tr><td>0002</td><td>4.000</td></tr></table>"
       ],
       "output_type": "pyout",
       "prompt_number": 9,
       "text": [
        "<Table rows=2 names=('a','b')>\n",
        "array([(1, 3.0), (2, 4.0)], \n",
        "      dtype=[('a', '|u1'), ('b', '<f2')])"
       ]
      }
     ],
     "prompt_number": 9
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Dtypes preserved\n",
      "print t['a'].dtype\n",
      "print t['b'].dtype"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "uint8\n",
        "float16\n"
       ]
      }
     ],
     "prompt_number": 10
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 10
    }
   ],
   "metadata": {}
  }
 ]
}