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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[Python Development]{Python Development}
\author[FOSSEE] {FOSSEE}
\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}
\date[] {8 November, 2009\\Day 2, Session 4}
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\AtBeginSection[]
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\begin{frame}<beamer>
\frametitle{Outline}
\Large
\tableofcontents[currentsection,currentsubsection]
\end{frame}
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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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% 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}
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}
\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{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}
\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{Summary}
We have covered:
\begin{itemize}
\item Following and Resolving Error Messages.
\item Exceptions.
\item Handling exceptions
\item Approach for Debugging.
% \item Writting and running tests.
\end{itemize}
\end{frame}
\end{document}
%% \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}
% \begin{frame}
% \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}
% \end{frame}
%
% \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}
% \end{frame}
%
% \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}
% \end{frame}
%
% %\begin{frame}[fragile]
% % \frametitle{Lets write some test!}
% %\begin{lstlisting}
% %#for form of equation y=mx+c
% %#given m and c for two equation,
% %#finding the intersection point.
% %def intersect(m1,c1,m2,c2):
% % x = (c2-c1)/(m1-m2)
% % y = m1*x+c1
% % return (x,y)
% %\end{lstlisting}
% %
% %Create a simple test for this
% %
% %function which will make it fail.
% %
% %\inctime{15}
% %\end{frame}
% %
%
% %% \begin{frame}[fragile]
% %% \frametitle{Exercise}
% %% Based on Euclid's algorithm:
% %% \begin{center}
% %% $gcd(a,b)=gcd(b,b\%a)$
% %% \end{center}
% %% gcd function can be written as:
% %% \begin{lstlisting}
% %% def gcd(a, b):
% %% if a%b == 0: return b
% %% return gcd(b, a%b)
% %% \end{lstlisting}
% %% \vspace*{-0.15in}
% %% \begin{block}{Task}
% %% \begin{itemize}
% %% \item Write at least
% %% two tests for above mentioned function.
% %% \item Write a non recursive implementation
% %% of gcd(), and test it using already
% %% written tests.
% %% \end{itemize}
% %% \end{block}
%
% %% \inctime{15}
% %% \end{frame}