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 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "String formatting"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "We have talked about strings before, and you know that it is possible to construct strings containing values, e.g."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "'x=' + str(43.2) + ', y=' + str(1./3.)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "However, one may want to format the values in more detail, for example forcing values to be a certain length, or have a certain number of decimal places. This is called *string formatting*."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "The syntax for formatting strings looks like this:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{0} {1} {2}\".format(1./3., 2./7., 2.)"
     ],
     "language": "python",
     "metadata": {
      "slideshow": {
       "slide_type": "-"
      }
     },
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "-"
      }
     },
     "source": [
      "In the above example, the ``0``, ``1``, and ``2`` refer to the position of the argument in the parentheses, so one could also do:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"The quantity {0} that could also be called {0} {1}\".format(1./3., 2./7.)"
     ],
     "language": "python",
     "metadata": {
      "slideshow": {
       "slide_type": "-"
      }
     },
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "By default, the value looks the same as if one had used ``str()``, but you can also specify the format and number of decimal places:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{0:10.3f}\".format(1./3.)"
     ],
     "language": "python",
     "metadata": {
      "slideshow": {
       "slide_type": "-"
      }
     },
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The ``f`` stands for floating-point, the 10 is the total length of the string, and the 3 is the nuber of decimal places."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "We can do something similar for integers (without the number of decimal places):"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{0:10d}\".format(4)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "There are a number of options for string formatting - for instance, one can add leading zeros:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{0:010d}\".format(4)"
     ],
     "language": "python",
     "metadata": {
      "slideshow": {
       "slide_type": "fragment"
      }
     },
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "fragment"
      }
     },
     "source": [
      "or align to the left:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{0:<10d}\".format(4)"
     ],
     "language": "python",
     "metadata": {
      "slideshow": {
       "slide_type": "fragment"
      }
     },
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "Instead of using ``0``, ``1``, etc. it is also possible to pass the values by name:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{day:02d}\".format(day=3)"
     ],
     "language": "python",
     "metadata": {
      "slideshow": {
       "slide_type": "fragment"
      }
     },
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {
      "slideshow": {
       "slide_type": "slide"
      }
     },
     "source": [
      "Here is an example of string formatting for a date:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "\"{year:04d}{month:02d}{day:02d}\".format(year=2013, month=7, day=8)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Exercise 1"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Write a function that takes year, month, day, hour, minutes, and seconds and converts them to a string with format ``2006-03-22 13:12:55``:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# your solution here"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Exercise 2"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Write a function that takes a string like ``2006-03-22 13:12:55`` and return the year, month, day, hour, minutes, and seconds as integers:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# your solution here"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}