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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:\\Advanced Python data structures, Functions and Debugging}

\author[FOSSEE Team] {Asokan Pichai\\Prabhu Ramachandran}

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

\date[] {10, October 2009\\Day 1, Session 4}

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

%% the beginning of each subsection:

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{

  \begin{frame}<beamer>

    \frametitle{Outline}

    \tableofcontents[currentsection,subsections]

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \titlepage

\end{frame}

\section{Advanced Data structures}

\subsection{Dictionary}

\begin{frame}{Dictionary}

  \begin{itemize}

    \item lists and tuples index: 0 \ldots n

    \item dictionaries index using strings

    \item \typ{ d = \{ ``Hitchhiker's guide'' : 42, ``Terminator'' : ``I'll be back''\}}

    \item \typ{d[``Terminator''] => ``I'll be back''}

    \item aka associative array, key-value pair, hashmap, hashtable \ldots    

    \item what can be keys?

  \end{itemize}

\end{frame}

\begin{frame}{Dictionary \ldots }

  \begin{itemize}

    \item \alert{Unordered}

      \begin{block}{Standard usage}

        for key in dict:\\

        \ \ \ \ print dict[key]

      \end{block}

    \item \typ{d.keys()} returns a list

    \item can we have duplicate keys?

  \end{itemize}

  \inctime{5}

\end{frame}

\begin{frame} {Problem Set 6.1}

  \begin{description}

\item[6.1.1] 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.

    \item[6.1.2] Count word frequencies in a file.

    \item[6.1.3] Find the most used Python keywords in your Python code (import keyword).

\end{description}

\inctime{10}

\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}

\inctime{5}

\end{frame}

\begin{frame}

  \frametitle{Problem set 6.2}

  \begin{description}

    \item[6.2.1] Given a dictionary of the names of students and their marks, identify how many duplicate marks are there? and what are these?

    \item[6.2.2] Given a string of the form ``4-7, 9, 12, 15'' find the numbers missing in this list for a given range.

\end{description}

\inctime{10}

\end{frame}

\section{Functions Reloaded!}

\begin{frame}[fragile]

    \frametitle{Advanced functions}

    \begin{itemize}

        \item default args

        \item var args

        \item keyword args

        \item scope

        \item \typ{global}

      \end{itemize}

\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{Keyword arguments}

\begin{frame}[fragile]

  \frametitle{Functions: keyword 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(prompt='?')

ask_ok(prompt='?', complaint='[y/n]')

ask_ok(complaint='[y/n]', prompt='?')

\end{lstlisting}

\inctime{15} 

\end{frame}

\section{Functional programming}

\begin{frame}[fragile]

    \frametitle{Functional programming}

    \begin{itemize}

      \item What is the basic idea?

      \item Why is it interesting?

      \item \typ{map, reduce, filter}

      \item list comprehension

      \item generators

    \end{itemize}

\end{frame}

\subsection{List comprehensions}

\begin{frame}[fragile]

    \frametitle{List Comprehensions}

Lets say we want to squares of all the numbers from 1 to 100

    \begin{lstlisting}

squares = []

for i in range(1, 100):

    squares.append(i * i)

    \end{lstlisting}

    \begin{lstlisting}

# list comprehension

squares = [i*i for i in range(1, 100)]

     \end{lstlisting}

Which is more readable?

\end{frame}

\begin{frame}[fragile]

    \frametitle{List Comprehensions}

What if you had a more complex function?

Lets say we want squares of numbers from 1 to 100 ending in 1, 2, 5, 7 only

    \begin{lstlisting}

squares = []

for i in range(1, 100):

    if i % 10 in [1, 2, 5, 7]:

        squares.append(i * i)

    \end{lstlisting}

    \begin{lstlisting}

# list comprehension

squares = [i*i for i in range(1, 100)

           if i % 10 in [1, 2, 5, 7]]

     \end{lstlisting}

Which is more readable?

\inctime{15}

\end{frame}

\section{Debugging}

\subsection{Errors and Exceptions}

\begin{frame}[fragile]

 \frametitle{Errors}

 \begin{lstlisting}

>>> while True print 'Hello world'

 \end{lstlisting}

\pause

  \begin{lstlisting}

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

    while True print 'Hello world'

                   ^

SyntaxError: invalid syntax

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

 \frametitle{Exceptions}

 \begin{lstlisting}

>>> print spam

\end{lstlisting}

\pause

\begin{lstlisting}

Traceback (most recent call last):

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

NameError: name 'spam' is not defined

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

 \frametitle{Exceptions}

 \begin{lstlisting}

>>> 1 / 0

\end{lstlisting}

\pause

\begin{lstlisting}

Traceback (most recent call last):

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

ZeroDivisionError: integer division 

or modulo by zero

\end{lstlisting}

\end{frame}

\subsection{Strategy}

\begin{frame}[fragile]

    \frametitle{Debugging effectively}

    \begin{itemize}

        \item \kwrd{print} based strategy

        \item Process:

    \end{itemize}

\pgfimage[interpolate=true,width=5cm,height=5cm]{DebugginDiagram.png}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Debugging effectively}

    \begin{itemize}

      \item Using \typ{\%debug} in IPython

    \end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{Debugging in IPython}

\small

\begin{lstlisting}

In [1]: import mymodule

In [2]: mymodule.test()

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

NameError   Traceback (most recent call last)

<ipython console> in <module>()

mymodule.py in test()

      1 def test():

----> 2     print spam

NameError: global name 'spam' is not defined

In [3]: %debug

> mymodule.py(2)test()

      0     print spam

ipdb> 

\end{lstlisting}

\inctime{15} 

\end{frame}

\subsection{Exercise}

\begin{frame}[fragile]

\frametitle{Debugging: Exercise}

\small

\begin{lstlisting}

import keyword

f = open('/path/to/file')

freq = {}

for line in f:

    words = line.split()

    for word in words:

        key = word.strip(',.!;?()[]: ')

        if keyword.iskeyword(key):

            value = freq[key]

            freq[key] = value + 1

print freq

\end{lstlisting}

\inctime{10}

\end{frame}

\begin{frame}

  \frametitle{What did we learn?}

  \begin{itemize}

    \item Dictionaries

    \item Sets

    \item Default and keyword arguments

    \item Functional Programming, list comprehensions

    \item Errors and Exceptions in Python

    \item Debugging: \%debug in IPython

  \end{itemize}

\end{frame}

\end{document}