%Tutorial slides on Python.

% Author: FOSSEE 

% Copyright (c) 2009, FOSSEE, IIT Bombay

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\title[Basic Python]{Python language: Data structures and functions}

\author[FOSSEE Team] {The FOSSEE Group}

\date[] {8 November, 2009\\Day 2, Session 3}

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  \titlepage

\section{Functions}

\subsection{Default arguments}

\begin{frame}[fragile]

  \frametitle{Functions: default arguments}

  \begin{lstlisting}

In []: greet = 'hello world'

In []: greet.split()

Out[]: ['hello', 'world']

In []: line = 'Rossum, Guido, 54, 46, 55'

In []: line.split(',')

Out[]: ['Rossum', ' Guido', ' 54',

                        ' 46', ' 55']

  \end{lstlisting}

\begin{frame}[fragile]

  \frametitle{Functions: default arguments \ldots}

  \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}

We have seen the following

  \begin{lstlisting}

In []: legend(['sin(2y)'],

              loc='center')

In []: plot(y, sin(y), 'g',

                 linewidth=2)

In []: annotate('local max',

                 xy=(1.5, 1))

In []: pie(science.values(),

            labels=science.keys())

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Functions: keyword arguments \ldots}

  \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}

\subsection{Built-in functions}

  {Before writing a function}

  \begin{itemize}

      \item Variety of builtin functions are available

      \item \typ{abs, any, all, len, max, min}

      \item \typ{pow, range, sum, type}

      \item Refer here:

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

  \end{itemize}

  \inctime{10} 

\end{frame}

\subsection{Exercises}

\begin{frame}{Problem set 3: Problem 3.1}

  Write a function to return the gcd of two numbers.

\begin{frame}{Problem 3.2}

Write a program to print all primitive pythagorean triads (a, b, c) where a, b are in the range 1---100 \\

A pythagorean triad $(a,b,c)$ has the property $a^2 + b^2 = c^2$.\\By primitive we mean triads that do not `depend' on others. For example, (4,3,5) is a variant of (3,4,5) and hence is not primitive. And (10,24,26) is easily derived from (5,12,13) and is also not primitive.

\end{frame}

\begin{frame}{Problem 3.3}

  Write a program that generates a list of all four digit numbers that have all their digits even and are perfect squares.\newline\\\emph{For example, the output should include 6400 but not 8100 (one digit is odd) or 4248 (not a perfect square).}

\inctime{15}

\end{frame}

\section{Modules}

\begin{frame}[fragile]

  \frametitle{\typ{from} \ldots \typ{import} magic}

  \begin{lstlisting}

from scipy.interpolate import splrep

from scipy.interpolate import splev

from scipy.integrate import quad

from scipy.integrate import odeint

from scipy.optimize import fsolve

  \end{lstlisting}

\emphbar{All the above statements import one function into your namespace}

\begin{frame}[fragile]

  \frametitle{Running scripts from command line}

  \small

  \begin{itemize}

    \item Start cmd

    \item cd to Desktop

    \item python sine\_plot.py

  \end{itemize}

  \pause

  \begin{lstlisting}

Traceback (most recent call last):

  File "sine_plot.py", line 1, in <module>

    x = linspace(-5*pi, 5*pi, 500)

NameError: name 'linspace' is not defined

  \end{lstlisting}

\begin{frame}[fragile]

  \frametitle{Remedy}

  \emphbar{Adding what lines to sine\_plot.py makes this program work?}

  \begin{lstlisting}

from scipy import *

  \end{lstlisting}

\alert{Now run python sine\_plot.py again!}

  \pause

  \begin{lstlisting}

Traceback (most recent call last):

  File "sine_plot.py", line 4, in <module>

    plot(x, x, 'b')

NameError: name 'plot' is not defined

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Remedy \ldots}

  \emphbar{What should we add now?}

  \begin{lstlisting}

from pylab import *

  \end{lstlisting}

\alert{Now run python sine\_plot.py again!!}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Modules}

  \begin{itemize}

    \item The \kwrd{import} keyword ``loads'' a module

    \item One can also use:

      \begin{lstlisting}

In []: from scipy import *

In []: from scipy import linspace

      \end{lstlisting}    

    \item What is the difference?

    \item \alert{Use the former only in interactive mode}

  \frametitle{Package hierarchies}

  \begin{lstlisting}

from scipy.interpolate import splev

from scipy.integrate import quad

from scipy.optimize import fsolve

  \end{lstlisting}

  \frametitle{from \ldots import in a conventional way!}

  \small

  \begin{lstlisting}

from scipy import linspace, pi, sin

from pylab import plot, legend, annotate

from pylab import xlim, ylim

x = linspace(-5*pi, 5*pi, 500)

plot(x, x, 'b')

plot(x, -x, 'b')

plot(x, sin(x), 'g', linewidth=2)

plot(x, x*sin(x), 'r', linewidth=3)

legend(['x', '-x', 'sin(x)', 'xsin(x)'])

annotate('origin', xy = (0, 0))

xlim(-5*pi, 5*pi)

ylim(-5*pi, 5*pi)

  \end{lstlisting}

  \frametitle{from \ldots import in a conventional way!}

  \small

  \begin{lstlisting}

import scipy

import pylab

x = scipy.linspace(-5*scipy.pi, 5*scipy.pi, 500)

pylab.plot(x, x, 'b')

pylab.plot(x, -x, 'b')

pylab.plot(x, scipy.sin(x), 'g', linewidth=2)

pylab.plot(x, x*scipy.sin(x), 'r', linewidth=3)

pylab.legend(['x', '-x', 'sin(x)', 'xsin(x)'])

pylab.annotate('origin', xy = (0, 0))

pylab.xlim(-5*scipy.pi, 5*scipy.pi)

pylab.ylim(-5*scipy.pi, 5*scipy.pi)

  \frametitle{Modules: Standard library}

  \item Very powerful, ``Batteries included''

  \item Some standard modules:

    \begin{itemize}

    \item Math: \typ{math}, \typ{random}

    \item Internet access: \typ{urllib2}, \typ{smtplib}

    \item System, Command line arguments: \typ{sys}

    \item Operating system interface: \typ{os}

    \item Regular expressions: \typ{re}

    \item Compression: \typ{gzip}, \typ{zipfile}, and \typ{tarfile}

    \item And a whole lot more!

    \end{itemize}

  \item Check out the Python Library reference:

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

  \end{itemize}

\inctime{5}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Modules of special interest}

  \begin{description}[matplotlibfor2d]

    \item[\typ{pylab}] Easy, interactive, 2D plotting

    \item[\typ{scipy}] arrays, statistics, optimization, integration, linear

            algebra, Fourier transforms, signal and image processing,

            genetic algorithms, ODE solvers, special functions, and more

    \item[\typ{Mayavi}] Easy, interactive, 3D plotting

  \end{description}

\end{frame}

\section{Objects}

\begin{frame}{Everything is an Object!}

  \begin{itemize}

    \item \typ{int}

    \item \typ{float}

    \item \typ{str}

    \item \typ{list}

    \item \typ{tuple}

    \item \typ{string}

    \item \typ{dictionary}

    \item \typ{function}

    \item User defined class is also an object!

  \end{itemize}

\end {frame}

\begin{frame}[fragile]

\frametitle{Using Objects}

  \begin{itemize}

    \item Creating Objects

    \begin{itemize}

      \item Initialization

    \end{itemize}

    \begin{lstlisting}

In []: a = str()

In []: b = "Hello World"

    \end{lstlisting}

    \item Object Manipulation

    \begin{itemize}

      \item Object methods

      \item ``.'' operator

    \end{itemize}

  \begin{lstlisting}

In []: "Hello World".split()

Out[]: ['Hello', 'World']

    \end{lstlisting}

\begin{frame}[fragile]

  \frametitle{Objects provide consistency}

  \small

  \begin{lstlisting}

for element in (1, 2, 3):

    print element

for key in {'one':1, 'two':2}:

    print key

for char in "123":

    print char

for line in open("myfile.txt"):

    print line

for line in urllib2.urlopen('http://site.com'):

    print line

  \end{lstlisting}

  \inctime{10}

\end{frame}

\begin{frame}

  \frametitle{What did we learn?}

  \begin{itemize}

    \item Functions: Default and Keyword arguments

    \item Modules

    \item Objects

  \end{itemize}

\end{frame}

\end{document}