1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     2 % Tutorial slides on Python.

     3 %

     4 % Author: Prabhu Ramachandran <prabhu at aero.iitb.ac.in>

     5 % Copyright (c) 2005-2008, Prabhu Ramachandran

     6 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     7 

     8 \documentclass[14pt,compress]{beamer}

     9 %\documentclass[draft]{beamer}

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    15 \mode<presentation>

    16 {

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    22 \usepackage[english]{babel}

    23 \usepackage[latin1]{inputenc}

    24 %\usepackage{times}

    25 \usepackage[T1]{fontenc}

    26 

    27 % Taken from Fernando's slides.

    28 \usepackage{ae,aecompl}

    29 \usepackage{mathpazo,courier,euler}

    30 \usepackage[scaled=.95]{helvet}

    31 

    32 \definecolor{darkgreen}{rgb}{0,0.5,0}

    33 

    34 \usepackage{listings}

    35 \lstset{language=Python,

    36     basicstyle=\ttfamily,

    37     commentstyle=\color{red}\itshape,

    38   stringstyle=\color{darkgreen},

    39   showstringspaces=false,

    40   keywordstyle=\color{blue}\bfseries}

    41 

    42 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    43 % Macros

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    53 

    54 \newcommand{\typ}[1]{\texttt{#1}}

    55 

    56 \newcommand{\kwrd}[1]{ \texttt{\textbf{\color{blue}{#1}}}  }

    57 

    58 %%% This is from Fernando's setup.

    59 % \usepackage{color}

    60 % \definecolor{orange}{cmyk}{0,0.4,0.8,0.2}

    61 % % Use and configure listings package for nicely formatted code

    62 % \usepackage{listings}

    63 % \lstset{

    64 %    language=Python,

    65 %    basicstyle=\small\ttfamily,

    66 %    commentstyle=\ttfamily\color{blue},

    67 %    stringstyle=\ttfamily\color{orange},

    68 %    showstringspaces=false,

    69 %    breaklines=true,

    70 %    postbreak = \space\dots

    71 % }

    72 

    73 

    74 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    75 % Title page

    76 \title[Basic Python]{Python:\\A great programming toolkit}

    77 

    78 \author[Asokan \& Prabhu] {Asokan Pichai\\Prabhu Ramachandran}

    79 

    80 \institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}

    81 \date[] {25, July 2009}

    82 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    83 

    84 %\pgfdeclareimage[height=0.75cm]{iitmlogo}{iitmlogo}

    85 %\logo{\pgfuseimage{iitmlogo}}

    86 

    87 

    88 %% Delete this, if you do not want the table of contents to pop up at

    89 %% the beginning of each subsection:

    90 \AtBeginSubsection[]

    91 {

    92   \begin{frame}<beamer>

    93     \frametitle{Outline}

    94     \tableofcontents[currentsection,currentsubsection]

    95   \end{frame}

    96 }

    97 

    98 

    99 % If you wish to uncover everything in a step-wise fashion, uncomment

   100 % the following command: 

   101 %\beamerdefaultoverlayspecification{<+->}

   102 

   103 %\includeonlyframes{current,current1,current2,current3,current4,current5,current6}

   104 

   105 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   106 % DOCUMENT STARTS

   107 \begin{document}

   108 

   109 \begin{frame}

   110   \titlepage

   111 \end{frame}

   112 \begin{frame}

   113   {Acknowledgements}

   114   \begin{center}

   115   This program is conducted by\\

   116   IIT, Bombay\\

   117   through CDEEP\\as part of  the open source initiatives\\

   118   under the aegis of\\

   119   \alert{National Mission on Education through ICT,} \\

   120   Ministry of HRD.

   121   \end{center}

   122 \end{frame}

   123 

   124 \begin{frame}

   125   \frametitle{Outline}

   126   \tableofcontents

   127   % You might wish to add the option [pausesections]

   128 \end{frame}

   129 

   130 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   131 % TODO

   132 %

   133 %  * Add slide on Python packages (modules)

   134 %  * Add slides on reference counting.

   135 

   136 \section{Agenda}

   137 \begin{frame}{About the Workshop}

   138   \begin{description}

   139 	\item[Session 1] Sat 14:00--15:55

   140 	\item[Session 2] Sat 16:05--18:00

   141 	\item[Session 3] Sun 14:00--15:55

   142 	\item[Session 4] Sun 16:05--18:00 

   143   \end{description}

   144 

   145   \begin{block}{Goal of the workshop}

   146 	At the end of this program, successful participants will be able to use python as their scripting and problem solving language. Aimed at Engg. students--focus on basic numerics and plotting-- but should serve a similar purpose for others. 

   147   \end{block}

   148 \end{frame}

   149 

   150 \begin{frame}{Checklist}

   151   Let us verify that all of us are having the same (similar) tools and environment

   152   \begin{description}

   153 	\item[python] Type python at the command line. Do you see version 2.5 or later?

   154 	\item[IPython] Is IPython available?

   155 	\item[Editor] Which editor? scite, vim, emacs, \ldots

   156   \end{description}

   157 \end{frame}

   158 

   159 \section{Overview}

   160 \begin{frame}{Session 1}

   161   \begin{itemize}

   162 	\item Introduction and motivation

   163 	\item Using the interpreter(s)

   164 	\item Basic data types: int, float, string

   165 	\item Basic data structures: list

   166 	\item Basic console IO: \texttt{raw\_input(), print}

   167     \item Basic control flow: \texttt{if, while}

   168 	\item Problem set 1

   169     \item Functions $\rightarrow$ Problem set 2

   170     \item lists, \texttt{for}  $\rightarrow$ Problem set 3

   171     \item IO, Modules $\rightarrow$ Problem sets 4,5, \ldots

   172   \end{itemize}

   173 \end{frame}

   174 

   175 \begin{frame}

   176   \frametitle{Introduction}

   177   \begin{itemize}

   178   \item Creator and BDFL: Guido van Rossum

   179   \item Conceived in December 1989

   180   \item ``Python'' as in Monty Python's Flying Circus

   181   \item Current stable version of Python is 2.6.x

   182   \item PSF license (like BSD: no strings attached)

   183   \item Highly cross platform

   184   \item Runs on the Nokia series 60!

   185   \item \alert{Philosophy:} Simple and complete by design

   186   \end{itemize}

   187 \end{frame}

   188 

   189 \begin{frame}

   190   \frametitle{Resources}

   191   \begin{itemize}

   192   \item Part of many GNU/Linux distributions

   193   \item Web: \url{http://www.python.org}

   194   \item Doc: \url{http://www.python.org/doc}

   195   \item Free Tutorials:

   196     \begin{itemize}

   197     \item Official Python tutorial: \url{http://docs.python.org/tut/tut.html}

   198     \item Byte of Python: \url{http://www.byteofpython.info/}

   199     \item Dive into Python: \url{http://diveintopython.org/}

   200     \end{itemize}

   201   \end{itemize}

   202 \end{frame}

   203 

   204 \begin{frame}

   205   \frametitle{Why Python?}

   206   \begin{itemize}

   207   \item Designed to be readable and easy to use

   208   \item High level, interpreted, modular, OO

   209   \item Much faster development cycle

   210   \item Powerful interactive environment

   211   \item Rapid application development

   212   \item Rich standard library and modules

   213   \item Interfaces well with C++, C and FORTRAN

   214   \item \alert{More than a math package $\Rightarrow$ some extra work compared to math packages}

   215   \end{itemize}

   216 \end{frame}

   217 

   218 \begin{frame}

   219   \frametitle{Use cases}

   220   \begin{itemize}

   221   \item NASA: Space Shuttle Mission Design

   222   \item AstraZeneca: Collaborative Drug Discovery

   223   \item ForecastWatch.com: Helps Meteorologists

   224   \item Industrial Light \& Magic: Runs on Python

   225   \item Zope: Commercial grade Toolkit

   226   \item Plone: Professional high feature CMS

   227   \item RedHat: install scripts, sys-admin tools

   228   \item Django: A great web application framework

   229   \item Google: A strong python shop

   230   \end{itemize}

   231 \end{frame}

   232 

   233 \begin{frame}

   234   \frametitle{To sum up, python is\ldots}

   235   \begin{itemize}

   236   \item dynamically typed, interpreted $\rightarrow$ rapid testing/prototyping

   237   \item powerful, very high level

   238   \item has full introspection 

   239   \item Did we mention powerful?

   240   \end{itemize}

   241   \begin{block}{But \ldots}

   242     may be wanting in performance. specialised resources such as SWIG, \alert{Cython} are available 

   243   \end{block}

   244   \inctime{15}

   245 \end{frame}

   246 

   247 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   248 % TIME: 15 m, running 15m

   249 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   250 

   251 \section{Python}

   252 

   253 \subsection{Getting Started}

   254 

   255 \begin{frame}[fragile]{At the prompt, type the following}

   256    \begin{lstlisting}

   257 >>> print 'Hello Python' 

   258 >>> print 3124 * 126789

   259 >>> 1786 % 12

   260 >>> 3124 * 126789

   261 >>> a = 3124 * 126789

   262 >>> big = 12345678901234567890 ** 3

   263 >>> verybig = big * big * big * big 

   264 >>> 12345**6, 12345**67, 12345**678

   265   \end{lstlisting}

   266 \end{frame}

   267 

   268 \begin{frame}[fragile]{At the prompt, type the following}

   269    \begin{lstlisting}

   270 >>> s = 'Hello '

   271 >>> p = 'World'

   272 >>> s + p 

   273 >>> s * 12 

   274 >>> s * s

   275 >>> s + p * 12, (s + p)* 12

   276 >>> s * 12 + p * 12

   277 >>> 12 * s 

   278     \end{lstlisting}

   279 \end{frame}

   280 

   281 \begin{frame}[fragile]{At the prompt, type the following}

   282   \begin{lstlisting}

   283 >>> 17/2

   284 >>> 17/2.0

   285 >>> 17.0/2

   286 >>> 17.0/8.5

   287 >>> int(17/2.0)

   288 >>> float(17/2)

   289 >>> str(17/2.0)

   290 >>> round( 7.5 )

   291   \end{lstlisting}

   292   \begin{block}{Mini exercise}

   293 	Round a float to the nearest integer, using \texttt{int()}?

   294   \end{block}

   295 \end{frame}

   296 

   297 \begin{frame}{Midi exercises}

   298   \begin{center}

   299     \begin{itemize}

   300       \item What does this do?

   301       \item \texttt{round(amount * 10) /10.0 }

   302     \end{itemize}

   303   \end{center}

   304 \end{frame}

   305 

   306 \begin{frame}{More exercises?}

   307   \begin{center}

   308     \begin{block}{Round sums}

   309       How to round a number to the nearest  5 paise?\\

   310       \begin{description}

   311         \item[Remember] 17.23 $\rightarrow$ 17.25,\\ while 17.22 $\rightarrow$ 17.20\\

   312       \end{description}

   313       How to round a number to the nearest 20 paise?

   314     \end{block}

   315   \end{center}

   316 \end{frame}

   317 

   318 \begin{frame}[fragile] {A question of good style}

   319   \begin{lstlisting}

   320     amount = 12.68

   321     denom = 0.05

   322     nCoins = round(amount/denom)

   323     rAmount = nCoins * denom

   324   \end{lstlisting}

   325   \pause

   326   \begin{block}{Style Rule \#1}

   327     Naming is 80\% of programming

   328   \end{block}

   329 \end{frame}

   330 

   331 

   332 \begin{frame}[fragile]

   333   \frametitle{Odds and ends}

   334   \begin{itemize}

   335     \item Case sensitive

   336     \item Dynamically typed $\Rightarrow$ need not specify a type

   337       \begin{lstlisting}

   338 a = 1

   339 a = 1.1

   340 a = "Now I am a string!"

   341       \end{lstlisting}

   342     \item Comments:

   343       \begin{lstlisting}

   344 a = 1  # In-line comments

   345 # Comment in a line to itself.

   346 a = "# This is not a comment!"

   347       \end{lstlisting}

   348   \end{itemize}

   349   \inctime{15}

   350 \end{frame}

   351 

   352 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   353 % TIME: 15 m, running 30m

   354 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   355 

   356 \subsection{Data types}

   357 \begin{frame}

   358   \frametitle{Basic types}

   359   \begin{itemize}

   360     \item numbers: float, int, long, complex

   361     \item strings

   362     \item boolean

   363   \end{itemize}

   364   \begin{block}{Also to be discussed later}

   365     tuples, lists, dictionaries, functions, objects\ldots

   366   \end{block}

   367 \end{frame}

   368 

   369 \begin{frame}[fragile]

   370   \frametitle{Numbers}

   371   \vspace*{-0.25in}

   372   \begin{lstlisting}

   373 >>> a = 1 # Int.

   374 >>> l = 1000000L # Long

   375 >>> e = 1.01325e5 # float

   376 >>> f = 3.14159 # float

   377 >>> c = 1+1j # Complex!

   378 >>> print f*c/a

   379 (3.14159+3.14159j)

   380 >>> print c.real, c.imag

   381 1.0 1.0

   382 >>> abs(c)

   383 1.4142135623730951

   384 >>> abs( 8 - 9.5 )

   385 1.5

   386   \end{lstlisting}

   387 \end{frame}

   388 

   389 \begin{frame}[fragile]

   390   \frametitle{Boolean}

   391   \begin{lstlisting}

   392 >>> t = True

   393 >>> f = not t

   394 False

   395 >>> f or t

   396 True

   397 >>> f and t

   398 False

   399   \end{lstlisting}

   400   \begin{block}{Try:}

   401   NOT True\\

   402   not TRUE

   403   \end{block}

   404 \end{frame}

   405 

   406 \begin{frame}[fragile]

   407   \frametitle{Relational and logical operators}

   408   \begin{lstlisting}

   409 >>> a, b, c = -1, 0, 1

   410 >>> a == b

   411 False

   412 >>> a <= b 

   413 True

   414 >>> a + b != c

   415 True

   416 >>> a < b < c

   417 True

   418 >>> c >= a + b

   419 True

   420   \end{lstlisting}

   421 \end{frame}

   422 

   423 \begin{frame}[fragile]

   424   \frametitle{Strings}

   425   \begin{lstlisting}

   426 s = 'this is a string'

   427 s = 'This one has "quotes" inside!'

   428 s = "I have 'single-quotes' inside!"

   429 l = "A string spanning many lines\

   430 one more line\

   431 yet another"

   432 t = """A triple quoted string does

   433 not need to be escaped at the end and 

   434 "can have nested quotes" etc."""

   435   \end{lstlisting}

   436 \end{frame}

   437 

   438 \begin{frame}[fragile]

   439   \frametitle{More Strings}

   440   \vspace*{-0.2in}

   441   \begin{lstlisting}

   442 >>> w = "hello"    

   443 >>> print w[0] + w[2] + w[-1]

   444 hlo

   445 >>> len(w) # guess what

   446 5

   447 >>> s = u'Unicode strings!'

   448 >>> # Raw strings (note the leading 'r')

   449 ... r_s = r'A string $\alpha \nu$'

   450   \end{lstlisting}

   451 \pause

   452   \begin{lstlisting}

   453 >>> w[0] = 'H' # Can't do that!

   454 Traceback (most recent call last):

   455   File "<stdin>", line 1, in ?

   456 TypeError: object does not support item assignment

   457   \end{lstlisting}

   458 \end{frame}

   459 

   460 \begin{frame}

   461   \frametitle{Let us switch to IPython}

   462   Why?

   463   \begin{block}

   464     {Better help (and a lot more)}

   465     Tab completion\\

   466     ?\\

   467     .?\\

   468     object.function?

   469   \end{block}

   470 \end{frame}

   471 

   472 \begin{frame}[fragile]

   473   \frametitle{More on strings}

   474   \begin{lstlisting}

   475 In [1]: a = 'hello world'

   476 In [2]: a.startswith('hell')

   477 Out[2]: True

   478 In [3]: a.endswith('ld')

   479 Out[3]: True

   480 In [4]: a.upper()

   481 Out[4]: 'HELLO WORLD'

   482 In [5]: a.upper().lower()

   483 Out[5]: 'hello world'

   484   \end{lstlisting}

   485 \end{frame}

   486 

   487 \begin{frame}[fragile]{Still with strings}

   488   \begin{lstlisting}

   489 In [6]: a.split()

   490 Out[6]: ['hello', 'world']

   491 In [7]: ''.join(['a', 'b', 'c'])

   492 Out[7]: 'abc'

   493 In [8] 'd' in ''.join( 'a', 'b', 'c')

   494 Out[8]: False

   495   \end{lstlisting}

   496   \begin{block}{Try:}

   497     \texttt{a.split( 'o' )}\\

   498     \texttt{'x'.join( a.split( 'o' ) )}

   499   \end{block}

   500 \end{frame}

   501 

   502 \begin{frame}[fragile]{Surprise! strings!!}

   503   \begin{lstlisting}

   504 In [11]: x, y = 1, 1.2

   505 In [12]: 'x is %s, y is %s' %(x, y)

   506 Out[12]: 'x is 1, y is 1.234'

   507   \end{lstlisting}

   508   \begin{block}{Try:}

   509     \texttt{'x is \%d, y is \%f' \%(x, y) }\\

   510     \texttt{'x is \%3d, y is \%4.2f' \%(x, y) }

   511   \end{block}

   512   \small

   513 \url{docs.python.org/lib/typesseq-strings.html}\\

   514 \end{frame}

   515 

   516 \begin{frame}

   517   {Interlude}

   518   \begin{block}

   519     {A classic problem}

   520     How to interchange values of two variables? Please note that the type of either variable is unknown and it is not necessary that both be of the same type even!

   521   \end{block}

   522   \inctime{30}

   523 \end{frame}

   524 

   525 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   526 % TIME: 25 m+ Interlude break 5 mins, running 60m 

   527 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   528 

   529 \subsection{Control flow}

   530 \begin{frame}

   531   \frametitle{Control flow constructs}  

   532   \begin{itemize}

   533   \item \kwrd{if/elif/else}: branching

   534   \item \kwrd{while}: looping

   535   \item \kwrd{for}: iterating 

   536   \item \kwrd{break, continue}: modify loop 

   537   \item \kwrd{pass}: syntactic filler

   538   \end{itemize}

   539 \end{frame}

   540 

   541 \begin{frame}[fragile]

   542   \frametitle{Basic conditional flow}

   543   \begin{lstlisting}

   544 In [21]: a = 7

   545 In [22]: b = 8

   546 In [23]: if a > b:

   547    ....:    print 'Hello'

   548    ....: else:

   549    ....:     print 'World'

   550    ....:

   551    ....:

   552 World

   553   \end{lstlisting}

   554   Let us switch to creating a file

   555 \end{frame}

   556 

   557 \begin{frame}

   558   {Creating python files}

   559   \begin{itemize}

   560     \item aka scripts

   561     \item use your editor

   562     \item Note that white space is the way to specify blocks!

   563     \item extension \typ{.py}

   564     \item run with \texttt{python hello.py} at the command line

   565     \item in IPython\ldots

   566   \end{itemize}

   567 \end{frame}

   568 

   569 \begin{frame}[fragile]

   570   \frametitle{\typ{If...elif...else} example}

   571 \begin{lstlisting}

   572 x = int(raw_input("Enter an integer:"))

   573 if x < 0:

   574      print 'Be positive!'

   575 elif x == 0:

   576      print 'Zero'

   577 elif x == 1:

   578      print 'Single'

   579 else:

   580      print 'More'

   581 \end{lstlisting}

   582 \end{frame}

   583 

   584 \begin{frame}{Simple IO}

   585   \begin{block}

   586     {Console Input}

   587     \texttt{raw\_input(}) waits for user input.\\Prompt string is optional.\\

   588     All keystrokes are Strings!\\\texttt{int()} converts string to int.

   589   \end{block}

   590   \begin{block}

   591     {Console output}

   592     \texttt{print} is straight forward. Major point to remember is the distinction between \texttt{print x} and \texttt{print x,}

   593   \end{block}

   594 \end{frame}

   595 

   596 \begin{frame}[fragile]

   597   \frametitle{Basic looping}

   598   \begin{lstlisting}

   599 # Fibonacci series:

   600 # the sum of two elements

   601 # defines the next

   602 a, b = 0, 1

   603 while b < 10:

   604     print b,

   605     a, b = b, a + b

   606  

   607 \end{lstlisting}

   608 \typ{1 1 2 3 5 8}\\  

   609 \alert{Recall it is easy to write infinite loops with \kwrd{while}}

   610   \inctime{20}

   611 \end{frame}

   612 

   613 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   614 % TIME: 20 m, running 80m 

   615 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   616 

   617 \begin{frame}

   618   \frametitle{Problem set 1}

   619   \begin{itemize}

   620     \item All the problems can be\\

   621       solved using \kwrd{if} and \kwrd{while} 

   622   \end{itemize}

   623 \end{frame}

   624 

   625 \begin{frame}{Problem 1.1}

   626   Write a program that displays all three digit numbers that are equal to the sum of the cubes of their digits. That is, print numbers $abc$ that have the property $abc = a^3 + b^3 + c^3$\\

   627 These are called $Armstrong$ numbers.

   628 \end{frame}

   629   

   630 \begin{frame}{Problem 1.2 - Collatz sequence}

   631 \begin{enumerate}

   632   \item Start with an arbitrary (positive) integer. 

   633   \item If the number is even, divide by 2; if the number is odd multiply by 3 and add 1.

   634   \item Repeat the procedure with the new number.

   635   \item It appears that for all starting values there is a cycle of 4, 2, 1 at which the procedure loops.

   636 \end{enumerate}

   637     Write a program that accepts the starting value and prints out the Collatz sequence.

   638 

   639 \end{frame}

   640 

   641 \begin{frame}{Problem 1.3 - Kaprekar's constant}

   642   \begin{enumerate}

   643     \item Take a four digit number--with at least two digits different.

   644     \item Arrange the digits in ascending and descending order, giving A and D respectively.

   645     \item Leave leading zeros in A!

   646     \item Subtract A from D.

   647     \item With the result, repeat from step 2.

   648   \end{enumerate}

   649   Write a program to accept a 4-digit number and display the progression to Kaprekar's constant.

   650 \end{frame}

   651 

   652 \begin{frame}[fragile]{Problem 1.4}

   653   Write a program that prints the following pyramid on the screen. 

   654   \begin{lstlisting}

   655 1

   656 2  2

   657 3  3  3

   658 4  4  4  4

   659   \end{lstlisting}

   660 The number of lines must be obtained from the user as input.\\

   661 \pause

   662 When can your code fail?

   663 \only<2->{\inctime{25}}

   664 \end{frame}

   665 

   666 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   667 % TIME: 25 m, running 105m 

   668 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   669 

   670 \subsection{Functions}

   671 \begin{frame}[fragile]

   672 \frametitle{Functions: examples}

   673   \begin{lstlisting}

   674 def signum( r ):

   675     """returns 0 if r is zero

   676     -1 if r is negative

   677     +1 if r is positive"""

   678     if r < 0:

   679         return -1

   680     elif r > 0:

   681         return 1

   682     else:

   683         return 0

   684   \end{lstlisting}

   685 \end{frame}

   686 

   687 \begin{frame}[fragile]

   688   \frametitle{Functions: examples}

   689   \begin{lstlisting}

   690 def pad( n, size ): 

   691     """pads integer n with spaces

   692     into a string of length size

   693     """

   694     SPACE = ' '

   695     s = str( n )

   696     padSize = size - len( s )

   697     return padSize * SPACE + s

   698   \end{lstlisting}

   699 \pause

   700 What about \%3d?

   701 \end{frame}

   702 

   703 \begin{frame}[fragile]

   704   {What does this function do?}

   705   \begin{lstlisting}

   706 def what( n ):

   707     if n < 0: n = -n

   708     while n > 0:

   709         if n % 2 == 1:

   710             return False

   711         n /= 10

   712     return True

   713   \end{lstlisting}

   714 \end{frame}

   715 

   716 \begin{frame}[fragile]

   717   {What does this function do?}

   718 \begin{lstlisting}

   719 def what( n ):

   720     i = 1    

   721     while i * i < n:

   722         i += 1

   723     return i * i == n, i

   724   \end{lstlisting}

   725 \end{frame}

   726 

   727 \begin{frame}[fragile]

   728   {What does this function do?}

   729   \begin{lstlisting}

   730 def what( n, x ):

   731     z = 1.0

   732     if n < 0:

   733         x = 1.0 / x

   734         n = -n

   735     while n > 0:

   736         if n % 2 == 1:

   737             z *= x

   738         n /= 2

   739         x *= x

   740     return z

   741   \end{lstlisting}

   742 \end{frame}

   743 

   744 \begin{frame}

   745   {Before writing a function}

   746   \begin{itemize}

   747       \item Builtin functions for various and sundry

   748       \item \typ{abs, any, all, len, max, min}

   749       \item \typ{pow, range, sum, type}

   750       \item Refer here:

   751           \url{http://docs.python.org/library/functions.html}

   752   \end{itemize}

   753   \inctime{15} 

   754 \end{frame}

   755 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   756 % TIME: 15 m, running 120m 

   757 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   758 

   759 \begin{frame}{Problem set 2}

   760   The focus is on writing functions and calling them.

   761 \end{frame}

   762 

   763 \begin{frame}{Problem 2.1}

   764   Write a function to return the gcd of two numbers.

   765 \end{frame}

   766 

   767 \begin{frame}{Problem 2.2}

   768 A pythagorean triad $(a,b,c)$ has the property $a^2 + b^2 = c^2$.\\By primitive we mean triads that do not `depend' on others. For example, (4,3,5) is a variant of (3,4,5) and hence is not primitive. And (10,24,26) is easily derived from (5,12,13) and should not be displayed by our program. \\

   769 Write a program to print primitive pythagorean triads. The program should generate all triads with a, b values in the range 0---100

   770 \end{frame}

   771 

   772 \begin{frame}{Problem 2.3}

   773   Write a program that generates a list of all four digit numbers that have all their digits even and are perfect squares.\\For example, the output should include 6400 but not 8100 (one digit is odd) or 4248 (not a perfect square).

   774 \end{frame}

   775 

   776 \begin{frame}{Problem 2.4}

   777   The aliquot of a number is defined as: the sum of the \emph{proper} divisors of the number. For example, the aliquot(12) = 1 + 2 + 3 + 4 + 6 = 16.\\

   778   Write a function that returns the aliquot number of a given number. 

   779 \end{frame}

   780 

   781 \begin{frame}{Problem 2.5}

   782   A pair of numbers (a, b) is said to be \alert{amicable} if the aliquot number of a is b and the aliquot number of b is a.\\

   783   Example: \texttt{220, 284}\\

   784   Write a program that prints all five digit amicable pairs.

   785   \inctime{30}

   786 \end{frame}

   787 

   788 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   789 % TIME: 30 m, running 150m 

   790 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   791 

   792 \subsection{Lists}

   793 

   794 \begin{frame}[fragile]

   795   \frametitle{List creation and indexing}

   796 \begin{lstlisting}

   797 >>> a = [] # An empty list.

   798 >>> a = [1, 2, 3, 4] # More useful.

   799 >>> len(a) 

   800 4

   801 >>> a[0] + a[1] + a[2] + a[-1]

   802 10

   803 \end{lstlisting}

   804   \begin{itemize}

   805   \item Indices start with ?

   806   \item Negative indices indicate ?

   807   \end{itemize}

   808 \end{frame}

   809 

   810 \begin{frame}[fragile]

   811   \frametitle{List: slices}

   812   \begin{itemize}

   813   \item Slicing is a basic operation

   814   \item \typ{list[initial:final:step]}

   815   \item  The step is optional

   816   \end{itemize}

   817 \begin{lstlisting}

   818 >>> a[1:3] # A slice.

   819 [2, 3]

   820 >>> a[1:-1]

   821 [2, 3, 4]

   822 >>> a[1:] == a[1:-1]

   823 False  

   824 \end{lstlisting}

   825 Explain last result

   826 \end{frame}

   827 

   828 \begin{frame}[fragile]

   829   \frametitle{List: more slices}

   830 \begin{lstlisting}

   831 >>> a[0:-1:2] # Notice the step!

   832 [1, 3]

   833 >>> a[::2]

   834 [1, 3]

   835 >>> a[-1::-1]

   836 \end{lstlisting}

   837 What do you think the last one will do?

   838   \emphbar{Note: Strings also use same indexing and slicing.}

   839 \end{frame}

   840 

   841 \begin{frame}[fragile]

   842   \frametitle{List: examples}

   843 \begin{lstlisting}

   844 >>> a = [1, 2, 3, 4]

   845 >>> a[:2]

   846 [1, 3]

   847 >>> a[0:-1:2]

   848 [1, 3]

   849 \end{lstlisting}

   850 \pause

   851 \alert{Lists are mutable (unlike strings)}

   852 \begin{lstlisting}

   853 >>> a[1] = 20

   854 >>> a

   855 [1, 20, 3, 4]

   856 \end{lstlisting}

   857 \end{frame}

   858 

   859 \begin{frame}[fragile]

   860   \frametitle{Lists are mutable and heterogenous}

   861 \begin{lstlisting}

   862 >>> a = ['spam', 'eggs', 100, 1234]

   863 >>> a[2] = a[2] + 23

   864 >>> a

   865 ['spam', 'eggs', 123, 1234]

   866 >>> a[0:2] = [1, 12] # Replace items

   867 >>> a

   868 [1, 12, 123, 1234]

   869 >>> a[0:2] = [] # Remove items

   870 >>> a.append( 12345 )

   871 >>> a

   872 [123, 1234, 12345]

   873 \end{lstlisting}

   874 \end{frame}

   875 

   876 \begin{frame}[fragile]

   877   \frametitle{List methods}

   878 \begin{lstlisting}

   879 >>> a = ['spam', 'eggs', 1, 12]

   880 >>> a.reverse() # in situ

   881 >>> a

   882 [12, 1, 'eggs', 'spam']

   883 >>> a.append(['x', 1]) 

   884 >>> a

   885 [12, 1, 'eggs', 'spam', ['x', 1]]

   886 >>> a.extend([1,2]) # Extend the list.

   887 >>> a.remove( 'spam' )

   888 >>> a

   889 [12, 1, 'eggs', ['x', 1], 1, 2]

   890 \end{lstlisting}

   891 \end{frame}

   892 

   893 \begin{frame}[fragile]

   894   \frametitle{List containership}

   895   \begin{lstlisting}

   896 >>> a = ['cat', 'dog', 'rat', 'croc']

   897 >>> 'dog' in a

   898 True

   899 >>> 'snake' in a

   900 False

   901 >>> 'snake' not in a

   902 True

   903 >>> 'ell' in 'hello world'

   904 True

   905   \end{lstlisting}

   906 \end{frame}

   907 

   908 \begin{frame}[fragile]

   909   \frametitle{Tuples: immutable}

   910 \begin{lstlisting}

   911 >>> t = (0, 1, 2)

   912 >>> print t[0], t[1], t[2], t[-1] 

   913 0 1 2 2

   914 >>> t[0] = 1

   915 Traceback (most recent call last):

   916   File "<stdin>", line 1, in ?

   917 TypeError: object does not support item

   918            assignment

   919 \end{lstlisting}  

   920 \begin{itemize}

   921     \item Multiple return values are actually a tuple.

   922     \item Exchange is tuple (un)packing

   923 \end{itemize}

   924 

   925 \end{frame}

   926 

   927 \begin{frame}[fragile]

   928   \frametitle{\typ{range()} function}

   929   \begin{lstlisting}

   930 >>> range(7)

   931 [0, 1, 2, 3, 4, 5, 6]

   932 >>> range( 3, 9)

   933 [3, 4, 5, 6, 7, 8]

   934 >>> range( 4, 17, 3)

   935 [4, 7, 10, 13, 16]

   936 >>> range( 5, 1, -1)

   937 [5, 4, 3, 2]

   938 >>> range( 8, 12, -1)

   939 []

   940   \end{lstlisting}

   941 \end{frame}

   942 

   943 \begin{frame}[fragile]

   944   \frametitle{\typ{for\ldots range(\ldots)} idiom}

   945   \begin{lstlisting}

   946 In [83]: for i in range(5):

   947    ....:     print i, i * i

   948    ....:     

   949    ....:     

   950 0 0

   951 1 1

   952 2 4

   953 3 9

   954 4 16

   955 \end{lstlisting}

   956 \end{frame}

   957 

   958 \begin{frame}[fragile]

   959   \frametitle{\typ{for}: the list companion}

   960   

   961   \begin{lstlisting}

   962 In [84]: a = ['a', 'b', 'c']

   963 In [85]: for x in a:

   964    ....:    print x, chr( ord(x) + 10 )

   965    ....:

   966 a  k

   967 b  l

   968 c  m

   969   \end{lstlisting}

   970   Iterating over the list and not the index + reference\\

   971   what if you want the index?

   972 \end{frame}

   973 

   974 \begin{frame}[fragile]

   975   \frametitle{\typ{for}: the list companion}

   976   \begin{lstlisting}

   977 In [89]: for p, ch in enumerate( a ):

   978    ....:     print p, ch

   979    ....:     

   980    ....:     

   981 0 a

   982 1 b

   983 2 c

   984   \end{lstlisting}

   985 Try: \typ{print enumerate(a)}

   986 \inctime{20}

   987 \end{frame}

   988 

   989 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   990 % TIME: 20 m, running 170m 

   991 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   992 

   993 \begin{frame}

   994   {Problem set 3}

   995   As you can guess, idea is to use \kwrd{for}!

   996 \end{frame}

   997 

   998 \begin{frame}{Problem 3.1}

   999   Which of the earlier problems is simpler when we use \kwrd{for} instead of \kwrd{while}? 

  1000 \end{frame}

  1001 

  1002 \begin{frame}{Problem 3.2}

  1003   Given an empty chessboard and one Bishop placed in any square, say (r, c), generate the list of all squares the Bishop could move to.

  1004 \end{frame}

  1005 

  1006 \begin{frame}[fragile]

  1007   \frametitle{Problem 3.3}

  1008 

  1009   Given two real numbers \typ{a, b}, and an integer \typ{N}, write a

  1010   function named \typ{linspace( a, b, N)} that returns an ordered list

  1011   of \typ{N} points starting with \typ{a} and ending in \typ{b} and

  1012   equally spaced.\\

  1013 

  1014   For example, \typ{linspace(0, 5, 11)}, should return, \\

  1015 \begin{lstlisting}

  1016 [ 0.0 ,  0.5,  1.0 ,  1.5,  2.0 ,  2.5,  

  1017   3.0 ,  3.5,  4.0 ,  4.5,  5.0 ]

  1018 \end{lstlisting}

  1019 \end{frame}

  1020 

  1021 \begin{frame}[fragile]

  1022   \frametitle{Problem 3.4a (optional)}

  1023 

  1024 Use the \typ{linspace} function and generate a list of N tuples of the form\\

  1025 \typ{[($x_1$,f($x_1$)),($x_2$,f($x_2$)),\ldots,($x_N$,f($x_N$))]}\\for the following functions,\begin{itemize}

  1026   \item \typ{f(x) = sin(x)}

  1027   \item \typ{f(x) = sin(x) + sin(10*x)}.

  1028 \end{itemize}

  1029 \end{frame}

  1030 

  1031 \begin{frame}[fragile]

  1032   \frametitle{Problem 3.4b (optional)}

  1033 

  1034   Using the tuples generated earlier, determine the intervals where the roots of the functions lie.

  1035 

  1036   \inctime{15}

  1037 \end{frame}

  1038 

  1039 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1040 % TIME: 15 m, running 185m 

  1041 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1042 

  1043 \subsection{IO}

  1044 

  1045 \begin{frame}[fragile]

  1046   \frametitle{Simple tokenizing and parsing}

  1047   \begin{lstlisting}

  1048 s = """The quick brown fox jumped

  1049        over the lazy dog"""

  1050 for word in s.split():

  1051     print word.capitalize()

  1052   \end{lstlisting}

  1053 \end{frame}

  1054 

  1055 \begin{frame}[fragile]

  1056   \frametitle{Problem 4.1}

  1057   Given a string like, ``1, 3-7, 12, 15, 18-21'', produce the list \\

  1058   \begin{lstlisting}

  1059     [1,3,4,5,6,7,12,15,18,19,20,21]

  1060   \end{lstlisting}

  1061 \end{frame}

  1062 

  1063 \begin{frame}[fragile]

  1064   \frametitle{File handling}

  1065 \begin{lstlisting}

  1066 >>> f = open('/path/to/file_name')

  1067 >>> data = f.read() # Read entire file.

  1068 >>> line = f.readline() # Read one line.

  1069 >>> f.close() # close the file.

  1070 \end{lstlisting}

  1071 Writing files

  1072 \begin{lstlisting}

  1073 >>> f = open('/path/to/file_name', 'w')

  1074 >>> f.write('hello world\n')

  1075 >>> f.close()

  1076 \end{lstlisting}

  1077 \begin{itemize}

  1078     \item Everything read or written is a string

  1079 \end{itemize}

  1080 \emphbar{Try \typ{file?} for more help}

  1081 \end{frame}

  1082 

  1083 \begin{frame}[fragile]

  1084     \frametitle{File and \kwrd{for}}

  1085 \begin{lstlisting}

  1086 >>> f = open('/path/to/file_name')

  1087 >>> for line in f:

  1088 ...     print line

  1089 ...

  1090 \end{lstlisting}

  1091 \end{frame}

  1092 

  1093 \begin{frame}{Problem 4.2}

  1094     The given file has lakhs of records in the form:\\

  1095     \typ{RGN;ID;NAME;MARK1;\ldots;MARK5;TOTAL;PFW}\\

  1096     Some entries may be empty.  Read the data from this file and print the

  1097     name of the student with the maximum total marks.

  1098 \end{frame}

  1099 

  1100 \begin{frame}{Problem 4.3}

  1101     For the same data file compute the average marks in different

  1102     subjects, the student with the maximum mark in each subject and also

  1103     the standard deviation of the marks.  Do this efficiently.

  1104 

  1105     \inctime{20}

  1106 \end{frame}

  1107 

  1108 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1109 % TIME: 20 m, running 205m 

  1110 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1111 

  1112 \subsection{Modules}

  1113 

  1114 \begin{frame}[fragile]

  1115     {Modules}

  1116 \begin{lstlisting}

  1117 >>> sqrt(2)

  1118 Traceback (most recent call last):

  1119   File "<stdin>", line 1, in <module>

  1120 NameError: name 'sqrt' is not defined

  1121 >>> import math        

  1122 >>> math.sqrt(2)

  1123 1.4142135623730951

  1124 \end{lstlisting}

  1125 \end{frame}

  1126 

  1127 \begin{frame}[fragile]

  1128     {Modules}

  1129   \begin{itemize}

  1130     \item The \kwrd{import} keyword ``loads'' a module

  1131     \item One can also use:

  1132       \begin{lstlisting}

  1133 >>> from math import sqrt

  1134 >>> from math import *

  1135       \end{lstlisting}    

  1136     \item What is the difference?