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%Tutorial slides on Python.

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

% Copyright (c) 2005-2009, Prabhu Ramachandran

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% Title page

\title[Basic Python]{Python language: Basics}

\author[FOSSEE Team] {The FOSSEE Group}

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

\date[] {1, November 2009\\Day 2, Session 1}

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%% the beginning of each subsection:

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    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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    \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{Data types}

\begin{frame}

  \frametitle{Primitive Data types}

  \begin{itemize}

    \item Numbers: float, int, complex

    \item Strings

    \item Boolean

  \end{itemize}

\end{frame}

\subsection{Numbers}

\begin{frame}[fragile]

  \frametitle{Numbers}

  \begin{itemize}

    \item \kwrd{int}\\ \kwrd{int} = whole number, no matter what the size!

  \begin{lstlisting}

In [1]: a = 13

In [2]: b = 99999999999999999999

  \end{lstlisting}

    \item \kwrd{float}

  \begin{lstlisting}

In [3]: fl = 3.141592

  \end{lstlisting}

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{Complex numbers}

  \begin{lstlisting}

In [1]: cplx = 3+4j

In [2]: abs(cplx)

Out[2]: 5.0

In [3]: cplx.imag

Out[3]: 4.0

In [4]: cplx.real

Out[4]: 3.0

  \end{lstlisting}

\end{frame}

\subsection{Boolean}

\begin{frame}[fragile]

  \frametitle{Boolean}

  \begin{lstlisting}

In [1]: t = True

In [2]: f = not t

Out[2]: False

In [3]: f or t

Out[3]: True

In [4]: f and t

Out[4]: False

  \end{lstlisting}

  \inctime{5}

\end{frame}

\subsection{Strings}

\begin{frame}[fragile]

  \frametitle{Strings}

Strings were introduced previously, let us now look at them in a little more detail.

  \begin{lstlisting}

In [1]: w = "hello"

In [2]: print w[0] + w[2] + w[-1]

Out[2]: hlo

In [3]: len(w) # guess what

Out[3]: 5

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Strings \ldots}

  \begin{lstlisting}

In [1]: w[0] = 'H' # Can't do that!

--------------------------------------------

TypeError  Traceback (most recent call last)

/<ipython console> in <module>()

TypeError: 'str' object does not

         support item assignment

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{String methods}

  \begin{lstlisting}

In [1]: a = 'Hello World'

In [2]: a.startswith('Hell')

Out[2]: True

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

Out[3]: True

In [4]: a.upper()

Out[4]: 'HELLO WORLD'

In [5]: a.lower()

Out[5]: 'hello world'

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Still with strings}

  \begin{itemize}

    \item We saw split() yesterday

    \item join() is the opposite of split()

  \end{itemize}

  \begin{lstlisting}

In [1]: ''.join(['a', 'b', 'c'])

Out[1]: 'abc'

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{String formatting}

  \begin{lstlisting}

In [1]: x, y = 1, 1.234

In [2]: 'x is %s, y is %s' %(x, y)

Out[2]: 'x is 1, y is 1.234'

  \end{lstlisting}

  \emphbar{\url{http://docs.python.org/library/stdtypes.html}}

  \inctime{10}

\end{frame}

\section{Operators}

\begin{frame}[fragile]

  \frametitle{Arithematic operators}

  \begin{lstlisting}

In [1]: 1786 % 12

Out[1]: 10

In [2]: 3124 * 126789

Out[2]: 396088836

In [3]: a = 3124 * 126789

In [4]: big = 1234567891234567890 ** 3

In [5]: verybig = big * big * big * big

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Arithematic operators \ldots}

  \begin{lstlisting}

In [1]: 17/2

Out[1]: 8

In [2]: 17/2.0

Out[2]: 8.5

In [3]: 17.0/2

Out[3]: 8.5

In [4]: 17.0/8.5

Out[4]: 2.0

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{String operations}

  \begin{lstlisting}

In [1]: s = 'Hello '

In [2]: p = 'World'

In [3]: s + p 

Out[3]: 'Hello World'

In [4]: s * 4

Out[4]: 'Hello Hello Hello Hello'

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{String operations \ldots}

  \begin{lstlisting}

In [1]: s * s

--------------------------------------------

TypeError  Traceback (most recent call last)

/<ipython console> in <module>()

TypeError: can't multiply sequence by

                non-int of type 'str'

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Relational and logical operators}

  \begin{lstlisting}

In [1]: pos, zer, neg = 1, 0, -1

In [2]: pos == neg

Out[2]: False

In [3]: pos >= neg

Out[3]: True

In [4]: neg < zer < pos

Out[4]: True

In [5]: pos + neg != zer

Out[5]: False

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Built-ins}

  \begin{lstlisting}

In [1]: int(17/2.0)

Out[1]: 8

In [2]: float(17/2)  # Recall

Out[2]: 8.0

In [3]: str(17/2.0)

Out[3]: '8.5'

In [4]: round( 7.5 )

Out[4]: 8.0

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Odds and ends}

  \begin{itemize}

    \item Case sensitive

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

      \begin{lstlisting}

In [1]: a = 1

In [2]: a = 1.1

In [3]: a = "Now I am a string!"

      \end{lstlisting}

    \item Comments:

      \begin{lstlisting}

In [4]: a = 1  # In-line comments

In [5]: # A comment line.

In [6]: a = "# Not a comment!"

      \end{lstlisting}

  \end{itemize}

  \inctime{15}

\end{frame}

\section{Simple IO}

\begin{frame}[fragile]

  \frametitle{Simple IO: Console Input}

  \begin{itemize}

    \item raw\_input() waits for user input.

      \begin{lstlisting}

In [1]: a = raw_input()

5

In [2]: a = raw_input('prompt > ')

prompt > 5

      \end{lstlisting}

    \item Prompt string is optional.

    \item All keystrokes are Strings!

    \item \texttt{int()} converts string to int.

  \end{itemize}

\end{frame}

\begin{frame}{Simple IO: Console output}

  \begin{itemize}

    \item \texttt{print} is straight forward

    \item Note the distinction between \texttt{print x} and \texttt{print x,}

  \end{itemize}

\end{frame}

\section{Control flow}

\begin{frame}

  \frametitle{Control flow constructs}  

  \begin{itemize}

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

  \item \kwrd{while}: looping

  \item \kwrd{for}: iterating 

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

  \item \kwrd{pass}: syntactic filler

  \end{itemize}

\end{frame}

\subsection{Basic Conditional flow}

\begin{frame}[fragile]

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

  \begin{lstlisting}

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

if x < 0:

     print 'Be positive!'

elif x == 0:

     print 'Zero'

elif x == 1:

     print 'Single'

else:

     print 'More'

  \end{lstlisting}

  \inctime{10}

\end{frame}

\subsection{Basic Looping}

\begin{frame}[fragile]

  \frametitle{\typ{while}}

Example: Fibonacci series

  \begin{lstlisting}

# the sum of two elements

# defines the next

a, b = 0, 1

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 range() returns a list of integers

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

  \item \emph{stop} argument is not included in the list

\end{itemize}

\end{frame}

\begin{frame}[fragile]

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

Example: print squares of first \typ{n} 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}

\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 as input.\\

\pause

\emphbar{When can your code fail?}

\inctime{5}

\end{frame}