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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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%% the beginning of each subsection:

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \titlepage

\end{frame}

\section{Python}

\subsection{Dictionary}

\begin{frame}{Dictionary}

  \begin{itemize}

    \item aka associative arrays, key-value pairs, hashmaps, hashtables \ldots    

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

    \item lists and tuples index: 0 \ldots n

    \item dictionaries index using strings

    \item aka key-value pairs

    \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:\\

            <use> dict[key] \# => value

      \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 2.1}

  \begin{description}

\item[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.

    \item[2.1.2] Count word frequencies in a file.

    \item[2.1.3] 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 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 numbers missing in this list for a given range.

\end{description}

\inctime{10}

\end{frame}

\subsection{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}

\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}

\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}

\subsection{Functional programming}

\begin{frame}[fragile]

    \frametitle{Functional programming}

What is the basic idea?\\

Why is it interesting?\\

\typ{map, reduce, filter}\\

list comprehension\\

generators

\end{frame}

\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}

\subsection{Debugging}

\begin{frame}[fragile]

 \frametitle{Errors}

 \begin{lstlisting}

>>> while True print 'Hello world'

  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

Traceback (most recent call last):

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

NameError: name 'spam' is not defined

>>> 1 / 0

Traceback (most recent call last):

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

ZeroDivisionError: integer division 

or modulo by zero

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Debugging effectively}

    \begin{itemize}

        \item  \kwrd{print} based strategy

        \item Process: Hypothesis, test, refine, rinse-repeat

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

    \end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{Debugging: example}

\small

\begin{lstlisting}

>>> import pdb

>>> import mymodule

>>> pdb.run('mymodule.test()')

> <string>(1)<module>()

(Pdb) continue

Traceback (most recent call last):

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

  File "/usr/lib/python2.6/pdb.py", line 1207, in run

    Pdb().run(statement, globals, locals)

  File "/usr/lib/python2.6/bdb.py", line 368, in run

    exec cmd in globals, locals

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

  File "mymodule.py", line 2, in test

    print spam

NameError: global name 'spam' is not defined

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Debugging in IPython}

\small

\begin{lstlisting}

In [1]: %pdb

Automatic pdb calling has been turned ON

In [2]: import mymodule

In [3]: mymodule.test()

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

NameError    Traceback (most recent call last)

/media/python/iitb/workshops/day1/<ipython console> in <module>()

/media/python/iitb/workshops/day1/mymodule.pyc in test()

      1 def test():

----> 2     print spam

NameError: global name 'spam' is not defined

> /media/python/iitb/workshops/day1/mymodule.py(2)test()

      0     print spam

ipdb>

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Debugging: Exercise}

\end{frame}

\begin{frame}

  \frametitle{What did we learn?}

\end{frame}

\end{document}