\newcommand{\typ}[1]{\lstinline{#1}}

\title[Python Development]{Python Development}

\date[] {8 November, 2009\\Day 2, Session 4}

    \frametitle{Outline}

      \Large

\section{Tests: Getting started}

\begin{frame}[fragile] 

  \frametitle{gcd revisited!}

  \begin{itemize}

  \item Open 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 python gcd.py

  \end{itemize}

\begin{frame}[fragile] 

  \frametitle{Find lcm using our gcd module}

  \begin{itemize}

  \item Open 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 python lcm.py

  \end{itemize}

  \begin{lstlisting}

5

4

56

  \end{lstlisting}    

\begin{frame}[fragile] 

  \frametitle{Writing stand-alone module}  

Edit 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 python gcd.py

  \item python lcm.py

  \end{itemize}

  \frametitle{More use of main}

  For 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]))

        assert gcd(x, y) == result

  \end{lstlisting}  

\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}

  \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}

\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{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}

 \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}

 \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

  \frametitle{Handling Exceptions}

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

  %%Revisiting the raw\_input

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

try:

    num = int(a)

    print num

except:

    if a == 'Q':

        print 'Exiting...'

    else:

        print 'Wrong input!'      

  \end{lstlisting}

\end{frame}

%% \begin{frame}[fragile]

%%   \frametitle{Solving it with \typ{try} and \typ{except}}

%% \vspace{-0.2in}

%%   \begin{lstlisting}

%% highest = 0

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

%%     fields = record.split(';')

%%     try:

%%         total = 0

%%         for score_str in fields[3:8]:

%%             score = int(score_str)

%%             total += score

%%         if total > highest:

%%             highest = total

%%     except:        

%%         pass

%% print highest

%%   \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}

    \frametitle{Debugging effectively}

    \begin{itemize}

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

    \end{itemize}

\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> 

\inctime{15} 

\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{Testing}

%%     \begin{itemize}

%%         \item Writing tests is really simple!

%%         \item Using nose.

%%         \item Example!

%%     \end{itemize}

%% \end{frame}

\section{Test Driven Approach}

    \frametitle{Need for Testing!}

    \begin{itemize}

        \item Quality

        \item Regression

        \item Documentation

    \end{itemize}

    %% \vspace*{0.25in}

    %% \emphbar{It is to assure that section of code is working as it is supposed to work}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Example}

    \begin{block}{Problem Statement}

      Write a function to check whether a given input

      string is a palindrome.

    \end{block}

\begin{frame}[fragile]

    \frametitle{Function: palindrome.py}

\begin{lstlisting}    

def is_palindrome(input_str):

  return input_str == input_str[::-1]

\end{lstlisting}    

\end{frame}

\begin{frame}[fragile]

    \frametitle{Test for the palindrome: palindrome.py}

\begin{lstlisting}    

def test_function_normal_words():

  input = "noon"

  assert is_palindrome(input) == True

if __name__ == "main'':

  test_function_normal_words()

\end{lstlisting}    

\end{frame}

\begin{frame}[fragile]

    \frametitle{Running the tests.}

\begin{lstlisting}    

$ nosetests palindrome.py 

.

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

Ran 1 test in 0.001s

OK

\end{lstlisting}    

\begin{frame}[fragile]

    \frametitle{Exercise: Including new tests.}

\begin{lstlisting}    

def test_function_ignore_cases_words():

  input = "Noon"

  assert is_palindrome(input) == True

\end{lstlisting}

     \vspace*{0.25in}

     Check\\

     \PythonCode{$ nosetests palindrome.py} \\

     \begin{block}{Task}

     Tweak the code to pass this test.

     \end{block}