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% Tutorial slides on Python.

%

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

% Copyright (c) 2005-2009, Prabhu Ramachandran

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% Title page

\title[Python Development]{Python Development}

\author[FOSSEE] {FOSSEE}

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

\date[] {1 May, 2010\\Day 2, Session 4}

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    \frametitle{Outline}

      \Large

    \tableofcontents[currentsection,currentsubsection]

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    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \maketitle

\end{frame}

\section{Tests: Getting started}

\begin{frame}[fragile] 

  \frametitle{gcd revisited!}

  \begin{itemize}

  \item Open \texttt{gcd.py}

  \end{itemize}  

\begin{lstlisting}

    def gcd(a, b):

        if a % b == 0: 

            return b

        return gcd(b, a%b)

    print gcd(15, 65)

    print gcd(16, 76)

\end{lstlisting}

  \begin{itemize}

  \item \texttt{python gcd.py}

  \end{itemize}

\end{frame}

\begin{frame}[fragile] 

  \frametitle{Find lcm using our gcd module}

  \begin{itemize}

  \item Open \texttt{lcm.py}  

  \item $lcm = \frac{a * b}{gcd(a,b)}$

  \end{itemize}  

\begin{lstlisting}

    from gcd import gcd    

    def lcm(a, b):

        return (a * b) / gcd(a, b)

    print lcm(14, 56)

\end{lstlisting}

  \begin{itemize}

  \item \texttt{python lcm.py}

  \end{itemize}

  \begin{lstlisting}

5

4

56

  \end{lstlisting}    

\end{frame}

\begin{frame}[fragile] 

  \frametitle{Writing stand-alone module}  

Edit \texttt{gcd.py} file to:

\begin{lstlisting}

    def gcd(a, b):

        if a % b == 0: 

            return b

        return gcd(b, a%b)

    if __name__ == "__main__":        

        print gcd(15, 65)

        print gcd(16, 76)

\end{lstlisting}

  \begin{itemize}

  \item \texttt{python gcd.py}

  \item \texttt{python lcm.py}

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Automating tests}

  \begin{lstlisting}

def gcd(a, b):

    if a % b == 0:

        return b

    return gcd(b, a % b)

if __name__ == '__main__':

    assert gcd(15, 65) == 5

    assert gcd(16, 76) == 4

  \end{lstlisting}  

\end{frame}

\begin{frame}[fragile]

  \frametitle{Automating tests}

  \begin{lstlisting}

if __name__ == '__main__':

    for line in open('numbers.txt'):

        numbers = line.split()

        x = int(numbers[0])

        y = int(numbers[1])

        result = int(numbers[2])

        if gcd(x, y) != result:

            print "Failed gcd test

                          for", x, y

  \end{lstlisting}  

\end{frame}

\begin{frame}[fragile]

  \frametitle{Python Test Packages}

    \begin{itemize}

\item Python's \typ{unittest}:\linebreak

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

\linebreak

\item \typ{nose}:\linebreak

  \url{http://code.google.com/p/python-nose/}

  \end{itemize}

\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.

        \item Play telephone with that line of code.

      \end{itemize}

\end{frame}

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

  \begin{lstlisting}

    amount = 12.68

    denom = 0.05

    num_coins = round(amount/denom)

    rounded_amount = num_coins * 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

        \item Consider any legible book

   \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}[fragile]

 \frametitle{Whitespace}

 Whitespace... it's not just for compilers!

  \begin{lstlisting}

def myfanfunc(somevar,another,yetmore):

    if a%b==0:return b

    return myfanfunc(b,a%b)

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

 \frametitle{Whitespace}

 The compiler doesn't care!  Humans do!

  \begin{lstlisting}

def my_fan_func(some_var, another, yet_more):

    if a % b == 0:

        return b

    return my_fan_func(b, a % b)

  \end{lstlisting}

\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}

\end{frame}

\begin{frame}{The Python Style Guide}

  \begin{itemize}

   \item PEP8

   \item PEP8

   \item PEP8

   \item \url{http://www.python.org/dev/peps/pep-0008/}

   \end{itemize}

\end{frame}

\section{Debugging}

\subsection{Errors and Exceptions}

\begin{frame}[fragile]

 \frametitle{Errors}

 \begin{lstlisting}

In []: 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}

In []: 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}

In []: 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}

\begin{frame}[fragile]

  \frametitle{Processing user input}

  \begin{lstlisting}

prompt = 'Enter a number(Q to quit): '

a = raw_input(prompt)

num = int(a) if a != 'Q' else 0

  \end{lstlisting}

  \emphbar{What if the user enters some other alphabet?}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Handling Exceptions}

  Python provides \typ{try} and \typ{except} clause.

  \begin{lstlisting}

prompt = 'Enter a number(Q to quit): '

a = raw_input(prompt)

try:

    num = int(a)

    print num

except:

    if a == 'Q':

        print "Exiting ..."

    else:

        print "Wrong input ..."

  \end{lstlisting}  

\end{frame}

\subsection{Strategy}

\begin{frame}[fragile]

    \frametitle{Debugging effectively}

    \begin{itemize}

        \item \typ{print} based strategy

        \item Process:

    \end{itemize}

\begin{center}

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

\end{center}

\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 []: import mymodule

In []: 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 []: %debug

> mymodule.py(2)test()

      0     print spam

ipdb> 

\end{lstlisting}

\inctime{15} 

\end{frame}

\begin{frame}

\frametitle{The Python Debugger}

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

\end{frame}

\subsection{Exercise}

\begin{frame}[fragile]

\frametitle{Debugging: Exercise}

\small

\begin{lstlisting}

science = {}

for record in open('sslc1.txt'):

    fields = record.split(';')

    region_code = fields[0].strip()

    score_str = fields[6].strip()

    score = int(score_str) if score_str != 'AA' 

                           else 0

    if score > 90:

        science[region_code] += 1

pie(science.values(), labels=science.keys())

savefig('science.png')

\end{lstlisting}

\inctime{10}

\end{frame}

\begin{frame}

 \frametitle{Documentation}

  \begin{itemize}

    \item Python: \linebreak

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

    \item Scipy \& Numpy: \linebreak

      \url{http://docs.scipy.org/doc/}

    \item IPython: \linebreak

      \url{http://ipython.scipy.org/moin/Documentation}

     \item Matplotlib: \linebreak

      \url{http://matplotlib.sourceforge.net/}

  \end{itemize}

\end{frame}