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%Tutorial slides on Python.

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% Author: FOSSEE 

% Copyright (c) 2009, FOSSEE, IIT Bombay

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% Title page

\title[Basic Python]{Python language: Data structures and functions}

\author[FOSSEE Team] {The FOSSEE Group}

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

\date[] {8 November, 2009\\Day 2, Session 2}

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

%% the beginning of each subsection:

\AtBeginSubsection[]

{

  \begin{frame}<beamer>

    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

  \end{frame}

}

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{

  \begin{frame}<beamer>

    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \titlepage

\end{frame}

\begin{frame}

  \frametitle{Outline}

  \tableofcontents

  % You might wish to add the option [pausesections]

\end{frame}

\section{Control flow}

\subsection{Basic Looping}

\begin{frame}[fragile]

  \frametitle{\typ{while}}

\begin{block}{Example: Fibonacci series}

  Sum of previous two elements defines the next

\end{block}

  \begin{lstlisting}

In []: a, b = 0, 1

In []: while b < 10:

  ...:     print b,

  ...:     a, b = b, a + b

  ...:

  ...:

\end{lstlisting}

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

\end{frame}

\begin{frame}[fragile]

\frametitle{\typ{range()}}

\kwrd{range([start,] stop[, step])}\\

\begin{itemize}

  \item \typ{range()} returns a list of integers

  \item The \typ{start} and the \typ{step} arguments are optional

  \item \typ{stop} is not included in the list

\end{itemize}

\vspace*{.5in}

\begin{block}{Documentation convention}

  \begin{itemize}

    \item \alert{Anything within \typ{[]} is optional}

    \begin{itemize}

      \item Nothing to do with Python.

    \end{itemize}

  \end{itemize}

\end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{\texttt{for} \ldots \typ{range()}}

Example: print squares of first \typ{5} numbers

  \begin{lstlisting}

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

 ....:     print i, i * i

 ....:

 ....:

0 0

1 1

2 4

3 9

4 16

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{\texttt{for} \ldots \typ{range()}}

Example: print squares of odd numbers from 3 to 9

  \begin{lstlisting}

In []: for i in range(3, 10, 2):

 ....:     print i, i * i

 ....:

 ....:

3 9

5 25

7 49

9 81

\end{lstlisting}

\inctime{5}

\end{frame}

\subsection{Exercises}

\begin{frame}{Problem set 1: Problem 1.1}

  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 $abc = a^3 + b^3 + c^3$\\

\vspace*{0.2in}

\emphbar{These are called $Armstrong$ numbers.}

\end{frame}

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

\begin{enumerate}

  \item Start with an arbitrary (positive) integer. 

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

  \item Repeat the procedure with the new number.

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

\end{enumerate}

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

\end{frame}

\begin{frame}[fragile]{Problem 1.3}

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

  \begin{lstlisting}

1

2  2

3  3  3

4  4  4  4

  \end{lstlisting}

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

\pause

\emphbar{When can your code fail?}

\inctime{5}

\end{frame}

\section{Data structures}

\subsection{Lists}

\begin{frame}[fragile]

  \frametitle{Lists}

\begin{block}{We already know that}

  \begin{lstlisting}

num = [1, 2, 3, 4]

  \end{lstlisting}

\centerline{is a list}

\end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Lists: methods}

  \begin{lstlisting}

In []: num = [1, 2, 3, 4]

In []: num + [9, 10, 11]

Out[]: [1, 2, 3, 4, 9, 10, 11]

In []: num.append([9, 10, 11])

In []: num

Out[]: [1, 2, 3, 4, [9, 10, 11]]

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Lists: methods}

  \begin{lstlisting}

In []: num = [1, 2, 3, 4]

In []: num.extend([5, 6, 7])

In []: num

Out[]: [1, 2, 3, 4, 5, 6, 7]

In []: num.reverse()

In []: num

Out[]: [7, 6, 5, 4, 3, 2, 1]

In []: num.remove(6)

In []: num

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Lists: slicing}

  \begin{itemize}

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

  \end{itemize}

\begin{lstlisting}

In []: a = [1, 2, 3, 4, 5]

In []: a[1:3]

Out[]: [2, 3]

In []: a[1:-1]

Out[]: [2, 3, 4]

In []: a[:3]

Out[]: [1, 2, 3]

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Lists: slicing}

  \begin{itemize}

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

  \end{itemize}

\begin{lstlisting}

In []: a[1:-1:2]

Out[]: [2, 4]

In []: a[::2]

Out[]: [1, 3, 5]

In []: a[-1::-1]

Out[]: [5, 4, 3, 2, 1]

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{List containership}

\begin{lstlisting}

In []: 4 in num

Out[]: True

In []: b = 15

In []: b in num

Out[]: False

In []: b not in num

Out[]: True

\end{lstlisting}

\end{frame}

\subsection{Tuples}

\begin{frame}[fragile]

\frametitle{Tuples: Immutable lists}

\begin{lstlisting}

In []: t = (1, 2, 3, 4, 5, 6, 7, 8)

In []: t[0] + t[3] + t[-1]

Out[]: 13

In []: t[4] = 7 

\end{lstlisting}

\pause

\begin{block}{Note:}

\begin{itemize}

  \item Tuples are immutable - cannot be changed

\end{itemize}

\end{block}

  \inctime{10}

\end{frame}

\begin{frame}

  {A classic problem}

  \begin{block}

    {Interchange values}

    How to interchange values of two variables? 

  \end{block}

  \pause

  \begin{block}{Note:}

    This Python idiom works for all types of variables.\\

They need not be of the same type!

  \end{block}

\end{frame}

\subsection{Dictionaries}

\begin{frame}[fragile]

  \frametitle{Dictionaries: recall}

  \begin{lstlisting}

In []: player = {'Mat': 134,'Inn': 233,

          'Runs': 10823, 'Avg': 52.53}

In []: player['Avg']

Out[]: 52.530000000000001

  \end{lstlisting}

  \begin{block}{Note!}

    Duplicate keys $\Rightarrow$ overwritten!\\

    You can iterate through a dictionary using keys.

  \end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Dictionaries: containership}

  \begin{lstlisting}

In []: 'Inn' in player

Out[]: True

In []: 'Econ' in player

Out[]: False

  \end{lstlisting}

  \begin{block}{Note}

    \begin{itemize}

      \item We can check for the containership of keys only

      \item Not values

    \end{itemize}

  \end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Dictionaries: methods}

  \begin{lstlisting}

In []: player.keys()

Out[]: ['Runs', 'Inn', 'Avg', 'Mat']

In []: player.values()

Out[]: [10823, 233, 

        52.530000000000001, 134]

  \end{lstlisting}

\end{frame}

\begin{frame} {Problem Set 2.1: Problem 2.1.1}

You are given date strings of the form ``29 Jul, 2009'', or ``4 January 2008''. In other words a number, a string and another number, with a comma sometimes separating the items.\\Write a function that takes such a string and returns a tuple (yyyy, mm, dd) where all three elements are ints.

\end{frame}

\subsection{Sets}

\begin{frame}[fragile]

  \frametitle{Sets}

    \begin{itemize}

      \item Simplest container, mutable

      \item No ordering, no duplicates

      \item usual suspects: union, intersection, subset \ldots

      \item >, >=, <, <=, in, \ldots

    \end{itemize}

    \begin{lstlisting}

In []: f10 = set([1,2,3,5,8])

In []: p10 = set([2,3,5,7])

In []: f10 | p10

Out[]: set([1, 2, 3, 5, 7, 8])

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Set \ldots}

    \begin{lstlisting}

In []: f10 & p10

Out[]: set([2, 3, 5])

In []: f10 - p10

Out[]: set([1, 8])

In []: p10 - f10, f10 ^ p10

Out[]: (set([7]), set([1, 7, 8]))

In []: set([2,3]) < p10

Out[]: True

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Set \ldots}

    \begin{lstlisting}

In []: set([2,3]) <= p10

Out[]: True

In []: 2 in p10

Out[]: True

In []: 4 in p10

Out[]: False

In []: len(f10)

Out[]: 5

\end{lstlisting}

\end{frame}

\begin{frame}

  \frametitle{Problem set 2.2: Problem 2.2.1}

Given a dictionary of the names of students and their marks, identify how many duplicate marks are there? and what are these?

\end{frame}

\begin{frame}

  \frametitle{Problem 2.2.2}

Given a list of words, find all the anagrams in the list.

\inctime{15}

\end{frame}

\section{Functions}

\begin{frame}[fragile]

  \frametitle{Functions}

  \begin{itemize}

    \item \kwrd{def} - keyword to define a function

    \item Arguments are local to a function

    \item Functions can return multiple values

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Functions: example}

  \begin{lstlisting}

def signum( r ):

    """returns 0 if r is zero

    -1 if r is negative

    +1 if r is positive"""

    if r < 0:

        return -1

    elif r > 0:

        return 1

    else:

        return 0

  \end{lstlisting}

  \emphbar{Note docstrings}

\end{frame}

\begin{frame}[fragile]

  \frametitle {What does this function do?}

  \begin{lstlisting}

def what( n ):

    if n < 0: n = -n

    while n > 0:

        if n % 2 == 1:

            return False

        n /= 10