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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: Data structures and functions}

\author[FOSSEE Team] {The FOSSEE Group}

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

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

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

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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{Data structures}

\subsection{Lists}

\begin{frame}[fragile]

  \frametitle{Lists}

\begin{block}{We already know that}

  \begin{lstlisting}

num = [1, 2, 3, 4, 5, 6, 7, 8]

  \end{lstlisting}

\centerline{is a list}

\end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Lists: methods}

  \begin{lstlisting}

In []: num.reverse()

In []: num

Out[]: [8, 7, 6, 5, 4, 3, 2, 1]

In []: num.extend([0, -1, -2])

In []: num

Out[]: [8, 7, 6, 5, 4, 3, 2, 1, 0, -1]

In []: num.remove(0)

In []: num

Out[]: [8, 7, 6, 5, 4, 3, 2, 1, -1]

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{List containership}

\begin{lstlisting}

In []: a = 8

In []: a in num

Out[]: True

In []: b = 10

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

\end{lstlisting}

\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 are not allowed!\\

    Dictionaries are iterable through keys.

  \end{block}

\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{Set}

\begin{frame}[fragile]

  \frametitle{Set}

    \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}

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

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

>>> f10|p10

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

>>> f10&p10

set([2, 3, 5])

>>> f10-p10

set([8, 1])

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Set}

    \begin{lstlisting}

>>> p10-f10, f10^p10

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

>>> set([2,3]) < p10

True

>>> set([2,3]) <= p10

True

>>> 2 in p10

True

>>> 4 in p10

False

>>> len(f10)

5

\end{lstlisting}

\end{frame}

\begin{frame}

  \frametitle{Problem set 2.2}

  \begin{description}

    \item[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?

    \item[2.2.2] Given a string of the form ``4-7, 9, 12, 15'' find the missing numbers in the given range.

\end{description}

\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 Docstrings are important!

    \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}

\end{frame}

\begin{frame}[fragile]

  {What does this function do?}

\begin{lstlisting}

def what( n ):

    i = 1

    while i * i < n:

        i += 1

    return i * i == n, i

  \end{lstlisting}

\end{frame}

\subsection{Default arguments}

\begin{frame}[fragile]

  \frametitle{Functions: default arguments}

  \small

  \begin{lstlisting}

def ask_ok(prompt, complaint='Yes or no!'):

    while True:

        ok = raw_input(prompt)

        if ok in ('y', 'ye', 'yes'): 

            return True

        if ok in ('n', 'no', 'nop',

                  'nope'): 

            return False

        print complaint

ask_ok('?')

ask_ok('?', '[Y/N]')

  \end{lstlisting}

\end{frame}

\subsection{Built-in functions}

\begin{frame}

  {Before writing a function}

  \begin{itemize}

      \item Variety of builtin functions are available

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

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

      \item Refer here:

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

  \end{itemize}

  \inctime{10} 

\end{frame}

\subsection{Exercises}

\begin{frame}{Problem set 3: Problem 3.1}

  Write a function to return the gcd of two numbers.

\end{frame}

\begin{frame}{Problem 3.2}

Write a program to print all primitive pythagorean triads (a, b, c) where a, b are in the range 1---100 \\

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 is also not primitive.

\end{frame}

\begin{frame}{Problem 3.3}

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

\inctime{15}

\end{frame}

\section{Modules}

\begin{frame}[fragile]

    {Modules}

\begin{lstlisting}

>>> sqrt(2)

Traceback (most recent call last):

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

NameError: name 'sqrt' is not defined

>>> import math        

>>> math.sqrt(2)

1.4142135623730951

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

    {Modules}

  \begin{itemize}

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

    \item One can also use:

      \begin{lstlisting}

>>> from math import sqrt

>>> from math import *

      \end{lstlisting}    

    \item What is the difference?

    \item \alert{Use the latter only in interactive mode}

    \end{itemize}

  \emphbar{Package hierarchies}

      \begin{lstlisting}

>>> from os.path import exists

      \end{lstlisting}

\end{frame}

\begin{frame}

  \frametitle{Modules: Standard library}

  \begin{itemize}

  \item Very powerful, ``Batteries included''

  \item Some standard modules:

    \begin{itemize}

    \item Math: \typ{math}, \typ{random}

    \item Internet access: \typ{urllib2}, \typ{smtplib}

    \item System, Command line arguments: \typ{sys}

    \item Operating system interface: \typ{os}

    \item Regular expressions: \typ{re}

    \item Compression: \typ{gzip}, \typ{zipfile}, and \typ{tarfile}

    \item And a whole lot more!

    \end{itemize}

  \item Check out the Python Library reference:

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

  \end{itemize}

\inctime{5}

\end{frame}

\section{Coding Style}

\begin{frame}{Readability and Consistency}

    \begin{itemize}

        \item Readability Counts!\\Code is read more often than its written.

        \item Consistency!

        \item Know when to be inconsistent.

      \end{itemize}

\end{frame}

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

  \begin{lstlisting}

    amount = 12.68

    denom = 0.05

    nCoins = round(amount/denom)

    rAmount = nCoins * denom

  \end{lstlisting}

  \pause

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

    Naming is 80\% of programming

  \end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Code Layout}

  \begin{itemize}

        \item Indentation

        \item Tabs or Spaces??

        \item Maximum Line Length

        \item Blank Lines

        \item Encodings

   \end{itemize}

\end{frame}

\begin{frame}{Whitespaces in Expressions}

  \begin{itemize}

        \item When to use extraneous whitespaces??

        \item When to avoid extra whitespaces??

        \item Use one statement per line

   \end{itemize}

\end{frame}

\begin{frame}{Comments}

  \begin{itemize}

        \item No comments better than contradicting comments

        \item Block comments

        \item Inline comments

   \end{itemize}

\end{frame}

\begin{frame}{Docstrings}

  \begin{itemize}

        \item When to write docstrings?

        \item Ending the docstrings

        \item One liner docstrings

   \end{itemize}

More information at PEP8: http://www.python.org/dev/peps/pep-0008/

\inctime{5}

\end{frame}

\section{Objects}

\begin{frame}{Objects in general}

    \begin{itemize}

        \item What is an Object? (Types and classes)

        \item identity

        \item type

        \item method

      \end{itemize}

\end{frame}

\begin{frame}{Almost everything is an Object!}

  \begin{itemize}

    \item \typ{list}

    \item \typ{tuple}

    \item \typ{string}

    \item \typ{dictionary}

    \item \typ{function}

    \item Of course, user defined class objects!

  \end{itemize}

\end {frame}

\begin{frame}{Using Objects}

  \begin{itemize}

    \item Creating Objects: Initialization

    \item Object Manipulation: Object methods and ``.'' operator

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Objects provide consistency}

  \small

  \begin{lstlisting}

for element in (1, 2, 3):

    print element

for key in {'one':1, 'two':2}:

    print key

for char in "123":

    print char

for line in open("myfile.txt"):

    print line

for line in urllib2.urlopen('http://site.com'):

    print line

  \end{lstlisting}

\inctime{10}

\end{frame}

\begin{frame}

  \frametitle{What did we learn?}

  \begin{itemize}

    \item Lists, Tuples, Dictionaries, Sets: creation and manipulation

    \item More about functions

    \item Coding style

    \item Objects: creation and manipulation

  \end{itemize}

\end{frame}

\end{document}