Python Training Notes - June 2012

0-python-training.ipynb

1-getting-started.ipynb

2-working-with-data.ipynb

3-classes.ipynb

{
 "metadata": {
  "name": "3-classes"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Classes"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Point:\n",
      "    x = 0 \n",
      "    y = 0"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1 = Point()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p2 = Point()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 4,
       "text": [
        "0"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.y"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 5,
       "text": [
        "0"
       ]
      }
     ],
     "prompt_number": 5
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p2.x, p2.y"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 6,
       "text": [
        "(0, 0)"
       ]
      }
     ],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.z"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "AttributeError",
       "evalue": "Point instance has no attribute 'z'",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
        "\u001b[0;32m<ipython-input-7-9f8bf4473cb3>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mp1\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mz\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
        "\u001b[0;31mAttributeError\u001b[0m: Point instance has no attribute 'z'"
       ]
      }
     ],
     "prompt_number": 7
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p3 = {\"x\": 0, \"y\": 0}\n",
      "p3[\"x\"]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 8,
       "text": [
        "0"
       ]
      }
     ],
     "prompt_number": 8
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 9,
       "text": [
        "0"
       ]
      }
     ],
     "prompt_number": 9
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def display_point(p):\n",
      "    print (p.x, p.y)\n",
      "    \n",
      "display_point(p1)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(0, 0)\n"
       ]
      }
     ],
     "prompt_number": 11
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.x = 1\n",
      "p1.y = 3\n",
      "display_point(p1)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(1, 3)\n"
       ]
      }
     ],
     "prompt_number": 12
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "display_point(p2)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(0, 0)\n"
       ]
      }
     ],
     "prompt_number": 13
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Point:\n",
      "    x = 0 \n",
      "    y = 0\n",
      "    \n",
      "    def display(p):\n",
      "        print (p.x, p.y)\n",
      "        \n",
      "p1 = Point()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 18
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "Point.display"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 22,
       "text": [
        "<unbound method Point.display>"
       ]
      }
     ],
     "prompt_number": 22
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "Point.display(p1)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(0, 0)\n"
       ]
      }
     ],
     "prompt_number": 19
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.display() # this is short hand for Point.display(p1)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(0, 0)\n"
       ]
      }
     ],
     "prompt_number": 21
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "Point.x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 23,
       "text": [
        "0"
       ]
      }
     ],
     "prompt_number": 23
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.x = 1"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 24
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "p1.x"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 25,
       "text": [
        "1"
       ]
      }
     ],
     "prompt_number": 25
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "Point.display(p1) "
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(1, 0)\n"
       ]
      }
     ],
     "prompt_number": 26
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "Point.x, Point.y"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 27,
       "text": [
        "(0, 0)"
       ]
      }
     ],
     "prompt_number": 27
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class Point:\n",
      "    def __init__(self, x=0, y=0):\n",
      "        self.x = x\n",
      "        self.y = y\n",
      "        \n",
      "    def display(self):\n",
      "        print (self.x, self.y)\n",
      "        \n",
      "    def distance_to(self, p2):\n",
      "        dx = self.x - p2.x\n",
      "        dy = self.y - p2.y\n",
      "        return (dx*dx+dy*dy) ** .5\n",
      "\n",
      "p1 = Point(2, 3)\n",
      "p1.display()\n",
      "\n",
      "p2 = Point()\n",
      "p2.display()\n",
      "\n",
      "print p1.distance_to(p2)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "(2, 3)\n",
        "(0, 0)\n",
        "3.60555127546\n"
       ]
      }
     ],
     "prompt_number": 31
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "**Example: Timer**"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import time\n",
      "class Timer:\n",
      "    def __init__(self):\n",
      "        self.elapsed = 0\n",
      "        self.numcalls = 0\n",
      "        \n",
      "    def start(self):\n",
      "        self.t0 = time.time()\n",
      "        self.numcalls += 1\n",
      "    \n",
      "    def stop(self):\n",
      "        t1 = time.time()\n",
      "        self.elapsed += t1 - self.t0\n",
      "        \n",
      "    def display(self):\n",
      "        print \"called\", self.numcalls, \"times and took\", self.elapsed, \"seconds\"\n",
      "\n",
      "t = Timer()\n",
      "t2 = Timer()\n",
      "for i in range(1000):\n",
      "    x = range(1000)\n",
      "    t.start()\n",
      "    'a' in x\n",
      "    t.stop()\n",
      "    \n",
      "    y = set(x)\n",
      "    t2.start()\n",
      "    'a' in y\n",
      "    t2.stop()\n",
      "    \n",
      "    \n",
      "t.display()\n",
      "t2.display()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "called 1000 times and took 0.0700263977051 seconds\n",
        "called 1000 times and took 0.0020649433136 seconds\n"
       ]
      }
     ],
     "prompt_number": 41
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "**Example: Formatting Text**"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%file formatting.py\n",
      "def format_file(filename, formatter):\n",
      "    text = open(filename).read()\n",
      "    print formatter.format(text)\n",
      "\n",
      "######\n",
      "    \n",
      "class UpperCaseFormatter:\n",
      "    def format(self, text):\n",
      "        return text.upper()\n",
      "    \n",
      "class LineFormatter:\n",
      "    def format(self, text):\n",
      "        lines = text.splitlines()\n",
      "        lines = [self.format_line(line) for line in lines]\n",
      "        return \"\\n\".join(lines)\n",
      "    \n",
      "    def format_line(self, line):\n",
      "        return line\n",
      "    \n",
      "class CenterAlignFormatter(LineFormatter):\n",
      "    def __init__(self, width):\n",
      "        self.width = width\n",
      "    def format_line(self, line):\n",
      "        return line.center(self.width)\n",
      "    \n",
      "format_file(\"a.txt\", CenterAlignFormatter(20))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Overwriting formatting.py\n"
       ]
      }
     ],
     "prompt_number": 54
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "!python formatting.py"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "        one         \r\n",
        "        two         \r\n",
        "       three        \r\n",
        "        four        \r\n",
        "        five        \r\n"
       ]
      }
     ],
     "prompt_number": 55
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Exceptions"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "x = [1,2,3]\n",
      "x[5]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "ename": "IndexError",
       "evalue": "list index out of range",
       "output_type": "pyerr",
       "traceback": [
        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mIndexError\u001b[0m                                Traceback (most recent call last)",
        "\u001b[0;32m<ipython-input-56-8e249bcb5a8c>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0mx\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;36m2\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;36m3\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0mx\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m5\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
        "\u001b[0;31mIndexError\u001b[0m: list index out of range"
       ]
      }
     ],
     "prompt_number": 56
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def readfile(filename):\n",
      "    try:\n",
      "        return open(filename).read()\n",
      "    except IOError:\n",
      "        return \"\"\n",
      "\n",
      "print readfile(\"nofile.txt\")"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "\n"
       ]
      }
     ],
     "prompt_number": 58
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "**Problem** Write function `listget` that takes a list, an index and a default value as arguments and returns the value at the specified index in the list if it exists or the default value. The last argument is optional and when not specified, `None` should be used.\n",
      "\n",
      "    >>> listget(['a', 'b', 'c'], 2, 'not-found')\n",
      "    'c'\n",
      "    >>> listget(['a', 'b', 'c'], 10, 'not-found')\n",
      "    'not-found'"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "**Problem** Write a function `safeint(s, default)`. It string `s` is can be converted to a number, it should be converted and returned. Otherwise, `default` should be returned.\n",
      "\n",
      "    >>> safeint(\"2\", 0)\n",
      "    2\n",
      "    >>> safeint(\"badnumber\", 0)\n",
      "    0"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def do_something():\n",
      "    1/2\n",
      "\n",
      "def cleanup():\n",
      "    pass\n",
      "\n",
      "try:\n",
      "    do_something()\n",
      "except:\n",
      "    print \"error\"\n",
      "else:\n",
      "    print \"success!\"\n",
      "finally:\n",
      "    cleanup()"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "success!\n"
       ]
      }
     ],
     "prompt_number": 66
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}

4-modules.ipynb