update_card_with_long_comment() PyFITS example

long_comment.ipynb

{
 "metadata": {
  "name": "long_comment"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import pyfits\n",
      "header = pyfits.Header()\n",
      "\n",
      "\n",
      "def update_card_with_long_comment(header, keyword, value, comment):\n",
      "    \"\"\"\n",
      "    Append/update a keyword in the given header such that if the comment\n",
      "    is too long to fit in a single card, instead append the comment in a\n",
      "    subsequent card with a blank keyword.\n",
      "    \"\"\"\n",
      "    \n",
      "    # Go ahead and add a keyword to the header *without* the comment\n",
      "    header[keyword] = value\n",
      "    \n",
      "    # Now we use the header.cards accessor to get the card object itself\n",
      "    # and find out how long it is\n",
      "    # The reason for the .rstrip() is to remove trailing spaces; otherwise\n",
      "    # the length will always be reported as 80\n",
      "    card = header.cards[keyword]\n",
      "    cardlen = len(str(card).rstrip())\n",
      "\n",
      "    # We need len(comment) + 3 spaces left in the card.\n",
      "    # The +3 is for ' / '\n",
      "    if pyfits.Card.length - (cardlen + 3) >= len(comment):\n",
      "        card.comment = comment\n",
      "    else:\n",
      "        # A single blank card can only hold up to 72 characters of comment\n",
      "        # text, so split the comment into 72 character chunks\n",
      "        idx = header.index(keyword)\n",
      "        while comment:\n",
      "            header.set('', comment[:72], after=idx)\n",
      "            comment = comment[72:]\n",
      "            idx += 1"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# First test a keyword with a short comment to see that it works normally\n",
      "update_card_with_long_comment(header, 'TEST1', 'VALUE1', 'A short comment')\n",
      "header"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 2,
       "text": [
        "TEST1   = 'VALUE1  '           / A short comment                                "
       ]
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Now let's test it out with a keyword that has a long comment\n",
      "update_card_with_long_comment(header, 'TEST2', 'VALUE2', 'Long comment ' * 5)\n",
      "header"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 3,
       "text": [
        "TEST1   = 'VALUE1  '           / A short comment                                \n",
        "TEST2   = 'VALUE2  '                                                            \n",
        "        Long comment Long comment Long comment Long comment Long comment        "
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Really long comment\n",
      "update_card_with_long_comment(header, 'TEST3', 'VALUE3', 'Long comment ' * 20)\n",
      "header"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 4,
       "text": [
        "TEST1   = 'VALUE1  '           / A short comment                                \n",
        "TEST2   = 'VALUE2  '                                                            \n",
        "TEST3   = 'VALUE3  '                                                            \n",
        "        Long comment Long comment Long comment Long comment Long comment Long co\n",
        "        mment Long comment Long comment Long comment Long comment Long comment L\n",
        "        ong comment Long comment Long comment Long comment Long comment Long com\n",
        "        ment Long comment Long comment Long comment                             \n",
        "        Long comment Long comment Long comment Long comment Long comment        "
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# One shortcoming of this is that there is now no way to be certain\n",
      "# that the blank keyword after TEST2 is actually tied to TEST2, so if\n",
      "# we call\n",
      "\n",
      "# update_card_with_long_comment(header, 'TEST2', 'VALUE2', 'Long comment ' * 5)\n",
      "\n",
      "# again the 'Long comment' card will be duplicated. There's no perfect way\n",
      "# around that I don't think.  But if you're just writing the header once this\n",
      "# shouldn't be a problem."
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 5
    }
   ],
   "metadata": {}
  }
 ]
}