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%Tutorial slides on Python.

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% Author: FOSSEE 

% Copyright (c) 2009, FOSSEE, IIT Bombay

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% Title page

\title[Basic Python]{Python language: Functions, modules and objects}

\author[FOSSEE Team] {The FOSSEE Group}

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

\date[] {SciPy.in 2010, Tutorials}

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    \frametitle{Outline}

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    \frametitle{Outline}

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \titlepage

\end{frame}

\begin{frame}

  \frametitle{Outline}

  \tableofcontents

  % You might wish to add the option [pausesections]

\end{frame}

\section{Functions}

\begin{frame}[fragile]

  \frametitle{Functions}

  \begin{itemize}

    \item \kwrd{def} - keyword to define a function

    \item Arguments are local to a function

    \item Functions can return multiple values

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Functions: example}

  \begin{lstlisting}

def signum( r ):

    """returns 0 if r is zero

    -1 if r is negative

    +1 if r is positive"""

    if r < 0:

        return -1

    elif r > 0:

        return 1

    else:

        return 0

  \end{lstlisting}

  \emphbar{Note docstrings}

\end{frame}

\begin{frame}[fragile]

  \frametitle {What does this function do?}

  \begin{lstlisting}

def what( n ):

    if n < 0: n = -n

    while n > 0:

        if n % 2 == 1:

            return False

        n /= 10

    return True

  \end{lstlisting}

\end{frame} 

\begin{frame}[fragile]

  {What does this function do?}

\begin{lstlisting}

def what( n ):

    i = 1

    while i * i < n:

        i += 1

    return i * i == n, i

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle {What does this function do?}

  \begin{lstlisting}

def what( x, n ):

    if n < 0: 

       n = -n

       x = 1.0 / x

    z = 1.0

    while n > 0:

        if n % 2 == 1:

            z *= x

        x *= x

        n /= 2

    return z

  \end{lstlisting}

\end{frame} 

\subsection{Exercises}

\begin{frame}{Problem 3.1}

  Write a function to return the gcd of two numbers.

\end{frame}

\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}

\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}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Functions: default arguments \ldots}

  \begin{lstlisting}

In []: def welcome(greet, name="World"):

  ....     print greet, name

In []: welcome("Hello")

Hello World

In []: welcome("Hi", "Guido")

Hi Guido

  \end{lstlisting}

\end{frame} 

\subsection{Keyword arguments}

\begin{frame}[fragile]

  \frametitle{Functions: Keyword arguments}

We have seen the following

\begin{lstlisting}

legend(['sin(2y)'], loc = 'center')

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

annotate('local max', xy = (1.5, 1))

pie(science.values(), 

            labels = science.keys())

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Functions: keyword arguments \ldots}

  \begin{lstlisting}

In []: def welcome(greet, name="World"):

  ....     print greet, name

In []: welcome("Hello", "James")

Hello James

In []: welcome("Hi", name="Guido")

Hi Guido

In []: welcome(name="Guido", greet="Hey")

Hey Guido

  \end{lstlisting}

\end{frame}

\subsection{Built-in functions}

\begin{frame}

  {Before writing a function}

  \begin{itemize}

      \item Variety of built-in 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}

\section{Modules}

\begin{frame}[fragile]

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

  \begin{lstlisting}

from scipy.integrate import odeint

from scipy.optimize import fsolve

  \end{lstlisting}

\emphbar{Above statements import a function to our namespace}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Running scripts from command line}

  \small

  \begin{itemize}

    \item Fire up a terminal

    \item python four\_plot.py

  \end{itemize}

  \pause

  \begin{lstlisting}

Traceback (most recent call last):

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

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

NameError: name 'linspace' is not defined

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Remedy \ldots}

  \begin{lstlisting}

from scipy import *

  \end{lstlisting}

\alert{Now run python four\_plot.py again}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Now what?}

  \begin{lstlisting}

Traceback (most recent call last):

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

    x = plot(x, x, 'b')

NameError: name 'plot' is not defined

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Remedy \ldots}

  \begin{lstlisting}

from pylab import *

  \end{lstlisting}

\alert{Now run python four\_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}

    \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{IPython namespace}

  \begin{lstlisting}

In [4]: whos

Interactive namespace is empty.

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{IPython namespace}

  \begin{lstlisting}

In [5]: from numpy import *

In [6]: whos

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Package hierarchies}

  \begin{lstlisting}

from scipy.integrate import odeint

from scipy.optimize import fsolve

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

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

\end{frame}

\begin{frame}[fragile]

  \frametitle{\typ{from} \ldots \typ{import} - 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)

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{\typ{import} - the community convention}

  \begin{lstlisting}

import numpy as np

np.linspace(-5 * np.pi, 5 * np.pi, 500)

import scipy as sp

sp.linspace(-5 * sp.pi, 5 * sp.pi, 500)

  \end{lstlisting}

\end{frame}

\begin{frame}

  \frametitle{Modules: Standard library}

  \begin{itemize}

  \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}

\begin{frame}[fragile]

  \frametitle{From which module?}

This plot function in pylab is cool, 

from where do I import it to include it in 

my\_nifty\_module.py?

\end{frame}

\begin{frame}[fragile]

  \frametitle{From which module?}

  \begin{lstlisting}

In [15]: plot.__module__

Out[15]: 'matplotlib.pyplot'

from matplotlib.pyplot import plot

  \end{lstlisting}

\end{frame}

\section{Objects}

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