diff -r 95fdc10975d5 -r 1725f25cd0d5 day1/Session-2.tex --- a/day1/Session-2.tex Sun Oct 04 17:03:10 2009 +0530 +++ b/day1/Session-2.tex Mon Oct 05 17:52:05 2009 +0530 @@ -2,7 +2,7 @@ % Tutorial slides on Python. % % Author: Prabhu Ramachandran -% Copyright (c) 2005-2008, Prabhu Ramachandran +% Copyright (c) 2005-2009, Prabhu Ramachandran %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \documentclass[14pt,compress]{beamer} @@ -33,7 +33,7 @@ \usepackage{listings} \lstset{language=Python, - basicstyle=\ttfamily, + basicstyle=\ttfamily\bfseries, commentstyle=\color{red}\itshape, stringstyle=\color{darkgreen}, showstringspaces=false, @@ -78,7 +78,7 @@ \author[Asokan \& Prabhu] {Asokan Pichai\\Prabhu Ramachandran} \institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay} -\date[] {25, July 2009} +\date[] {10, October 2009} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %\pgfdeclareimage[height=0.75cm]{iitmlogo}{iitmlogo} @@ -109,511 +109,10 @@ \begin{frame} \titlepage \end{frame} -\begin{frame} - {Acknowledgements} - \begin{center} - This program is conducted by\\ - IIT, Bombay\\ - through CDEEP\\as part of the open source initiatives\\ - under the aegis of\\ - \alert{National Mission on Education through ICT,} \\ - Ministry of HRD. - \end{center} -\end{frame} - -\begin{frame} - \frametitle{Outline} - \tableofcontents - % You might wish to add the option [pausesections] -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TODO -% -% * Add slide on Python packages (modules) -% * Add slides on reference counting. - -\section{Agenda} -\begin{frame}{About the Workshop} - \begin{description} - \item[Session 1] Sat 14:00--15:55 - \item[Session 2] Sat 16:05--18:00 - \item[Session 3] Sun 14:00--15:55 - \item[Session 4] Sun 16:05--18:00 - \end{description} - - \begin{block}{Goal of the workshop} - At the end of this program, successful participants will be able to use python as their scripting and problem solving language. Aimed at Engg. students--focus on basic numerics and plotting-- but should serve a similar purpose for others. - \end{block} -\end{frame} - -\begin{frame}{Checklist} - Let us verify that all of us are having the same (similar) tools and environment - \begin{description} - \item[python] Type python at the command line. Do you see version 2.5 or later? - \item[IPython] Is IPython available? - \item[Editor] Which editor? scite, vim, emacs, \ldots - \end{description} -\end{frame} - -\section{Overview} -\begin{frame}{Session 1} - \begin{itemize} - \item Introduction and motivation - \item Using the interpreter(s) - \item Basic data types: int, float, string - \item Basic data structures: list - \item Basic console IO: \texttt{raw\_input(), print} - \item Basic control flow: \texttt{if, while} - \item Problem set 1 - \item Functions $\rightarrow$ Problem set 2 - \item lists, \texttt{for} $\rightarrow$ Problem set 3 - \item IO, Modules $\rightarrow$ Problem sets 4,5, \ldots - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{Introduction} - \begin{itemize} - \item Creator and BDFL: Guido van Rossum - \item Conceived in December 1989 - \item ``Python'' as in Monty Python's Flying Circus - \item Current stable version of Python is 2.6.x - \item PSF license (like BSD: no strings attached) - \item Highly cross platform - \item Runs on the Nokia series 60! - \item \alert{Philosophy:} Simple and complete by design - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{Resources} - \begin{itemize} - \item Part of many GNU/Linux distributions - \item Web: \url{http://www.python.org} - \item Doc: \url{http://www.python.org/doc} - \item Free Tutorials: - \begin{itemize} - \item Official Python tutorial: \url{http://docs.python.org/tut/tut.html} - \item Byte of Python: \url{http://www.byteofpython.info/} - \item Dive into Python: \url{http://diveintopython.org/} - \end{itemize} - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{Why Python?} - \begin{itemize} - \item Designed to be readable and easy to use - \item High level, interpreted, modular, OO - \item Much faster development cycle - \item Powerful interactive environment - \item Rapid application development - \item Rich standard library and modules - \item Interfaces well with C++, C and FORTRAN - \item \alert{More than a math package $\Rightarrow$ some extra work compared to math packages} - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{Use cases} - \begin{itemize} - \item NASA: Space Shuttle Mission Design - \item AstraZeneca: Collaborative Drug Discovery - \item ForecastWatch.com: Helps Meteorologists - \item Industrial Light \& Magic: Runs on Python - \item Zope: Commercial grade Toolkit - \item Plone: Professional high feature CMS - \item RedHat: install scripts, sys-admin tools - \item Django: A great web application framework - \item Google: A strong python shop - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{To sum up, python is\ldots} - \begin{itemize} - \item dynamically typed, interpreted $\rightarrow$ rapid testing/prototyping - \item powerful, very high level - \item has full introspection - \item Did we mention powerful? - \end{itemize} - \begin{block}{But \ldots} - may be wanting in performance. specialised resources such as SWIG, \alert{Cython} are available - \end{block} - \inctime{15} -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 15 m, running 15m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \section{Python} -\subsection{Getting Started} - -\begin{frame}[fragile]{At the prompt, type the following} - \begin{lstlisting} ->>> print 'Hello Python' ->>> print 3124 * 126789 ->>> 1786 % 12 ->>> 3124 * 126789 ->>> a = 3124 * 126789 ->>> big = 12345678901234567890 ** 3 ->>> verybig = big * big * big * big ->>> 12345**6, 12345**67, 12345**678 - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile]{At the prompt, type the following} - \begin{lstlisting} ->>> s = 'Hello ' ->>> p = 'World' ->>> s + p ->>> s * 12 ->>> s * s ->>> s + p * 12, (s + p)* 12 ->>> s * 12 + p * 12 ->>> 12 * s - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile]{At the prompt, type the following} - \begin{lstlisting} ->>> 17/2 ->>> 17/2.0 ->>> 17.0/2 ->>> 17.0/8.5 ->>> int(17/2.0) ->>> float(17/2) ->>> str(17/2.0) ->>> round( 7.5 ) - \end{lstlisting} - \begin{block}{Mini exercise} - Round a float to the nearest integer, using \texttt{int()}? - \end{block} -\end{frame} - -\begin{frame}{Midi exercises} - \begin{center} - \begin{itemize} - \item What does this do? - \item \texttt{round(amount * 10) /10.0 } - \end{itemize} - \end{center} -\end{frame} - -\begin{frame}{More exercises?} - \begin{center} - \begin{block}{Round sums} - How to round a number to the nearest 5 paise?\\ - \begin{description} - \item[Remember] 17.23 $\rightarrow$ 17.25,\\ while 17.22 $\rightarrow$ 17.20\\ - \end{description} - How to round a number to the nearest 20 paise? - \end{block} - \end{center} -\end{frame} - -\begin{frame}[fragile] {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{Odds and ends} - \begin{itemize} - \item Case sensitive - \item Dynamically typed $\Rightarrow$ need not specify a type - \begin{lstlisting} -a = 1 -a = 1.1 -a = "Now I am a string!" - \end{lstlisting} - \item Comments: - \begin{lstlisting} -a = 1 # In-line comments -# Comment in a line to itself. -a = "# This is not a comment!" - \end{lstlisting} - \end{itemize} - \inctime{15} -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 15 m, running 30m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -\subsection{Data types} -\begin{frame} - \frametitle{Basic types} - \begin{itemize} - \item numbers: float, int, long, complex - \item strings - \item boolean - \end{itemize} - \begin{block}{Also to be discussed later} - tuples, lists, dictionaries, functions, objects\ldots - \end{block} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Numbers} - \vspace*{-0.25in} - \begin{lstlisting} ->>> a = 1 # Int. ->>> l = 1000000L # Long ->>> e = 1.01325e5 # float ->>> f = 3.14159 # float ->>> c = 1+1j # Complex! ->>> print f*c/a -(3.14159+3.14159j) ->>> print c.real, c.imag -1.0 1.0 ->>> abs(c) -1.4142135623730951 ->>> abs( 8 - 9.5 ) -1.5 - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Boolean} - \begin{lstlisting} ->>> t = True ->>> f = not t -False ->>> f or t -True ->>> f and t -False - \end{lstlisting} - \begin{block}{Try:} - NOT True\\ - not TRUE - \end{block} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Relational and logical operators} - \begin{lstlisting} ->>> a, b, c = -1, 0, 1 ->>> a == b -False ->>> a <= b -True ->>> a + b != c -True ->>> a < b < c -True ->>> c >= a + b -True - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Strings} - \begin{lstlisting} -s = 'this is a string' -s = 'This one has "quotes" inside!' -s = "I have 'single-quotes' inside!" -l = "A string spanning many lines\ -one more line\ -yet another" -t = """A triple quoted string does -not need to be escaped at the end and -"can have nested quotes" etc.""" - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{More Strings} - \vspace*{-0.2in} - \begin{lstlisting} ->>> w = "hello" ->>> print w[0] + w[2] + w[-1] -hlo ->>> len(w) # guess what -5 ->>> s = u'Unicode strings!' ->>> # Raw strings (note the leading 'r') -... r_s = r'A string $\alpha \nu$' - \end{lstlisting} -\pause - \begin{lstlisting} ->>> w[0] = 'H' # Can't do that! -Traceback (most recent call last): - File "", line 1, in ? -TypeError: object does not support item assignment - \end{lstlisting} -\end{frame} - -\begin{frame} - \frametitle{Let us switch to IPython} - Why? - \begin{block} - {Better help (and a lot more)} - Tab completion\\ - ?\\ - .?\\ - object.function? - \end{block} -\end{frame} - -\begin{frame}[fragile] - \frametitle{More on strings} - \begin{lstlisting} -In [1]: a = 'hello world' -In [2]: a.startswith('hell') -Out[2]: True -In [3]: a.endswith('ld') -Out[3]: True -In [4]: a.upper() -Out[4]: 'HELLO WORLD' -In [5]: a.upper().lower() -Out[5]: 'hello world' - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile]{Still with strings} - \begin{lstlisting} -In [6]: a.split() -Out[6]: ['hello', 'world'] -In [7]: ''.join(['a', 'b', 'c']) -Out[7]: 'abc' -In [8] 'd' in ''.join( 'a', 'b', 'c') -Out[8]: False - \end{lstlisting} - \begin{block}{Try:} - \texttt{a.split( 'o' )}\\ - \texttt{'x'.join( a.split( 'o' ) )} - \end{block} -\end{frame} - -\begin{frame}[fragile]{Surprise! strings!!} - \begin{lstlisting} -In [11]: x, y = 1, 1.2 -In [12]: 'x is %s, y is %s' %(x, y) -Out[12]: 'x is 1, y is 1.234' - \end{lstlisting} - \begin{block}{Try:} - \texttt{'x is \%d, y is \%f' \%(x, y) }\\ - \texttt{'x is \%3d, y is \%4.2f' \%(x, y) } - \end{block} - \small -\url{docs.python.org/lib/typesseq-strings.html}\\ -\end{frame} - -\begin{frame} - {Interlude} - \begin{block} - {A classic problem} - How to interchange values of two variables? Please note that the type of either variable is unknown and it is not necessary that both be of the same type even! - \end{block} - \inctime{30} -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 25 m+ Interlude break 5 mins, running 60m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -\subsection{Control flow} -\begin{frame} - \frametitle{Control flow constructs} - \begin{itemize} - \item \kwrd{if/elif/else}: branching - \item \kwrd{while}: looping - \item \kwrd{for}: iterating - \item \kwrd{break, continue}: modify loop - \item \kwrd{pass}: syntactic filler - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Basic conditional flow} - \begin{lstlisting} -In [21]: a = 7 -In [22]: b = 8 -In [23]: if a > b: - ....: print 'Hello' - ....: else: - ....: print 'World' - ....: - ....: -World - \end{lstlisting} - Let us switch to creating a file -\end{frame} - -\begin{frame} - {Creating python files} - \begin{itemize} - \item aka scripts - \item use your editor - \item Note that white space is the way to specify blocks! - \item extension \typ{.py} - \item run with \texttt{python hello.py} at the command line - \item in IPython\ldots - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{\typ{If...elif...else} example} -\begin{lstlisting} -x = int(raw_input("Enter an integer:")) -if x < 0: - print 'Be positive!' -elif x == 0: - print 'Zero' -elif x == 1: - print 'Single' -else: - print 'More' -\end{lstlisting} -\end{frame} - -\begin{frame}{Simple IO} - \begin{block} - {Console Input} - \texttt{raw\_input(}) waits for user input.\\Prompt string is optional.\\ - All keystrokes are Strings!\\\texttt{int()} converts string to int. - \end{block} - \begin{block} - {Console output} - \texttt{print} is straight forward. Major point to remember is the distinction between \texttt{print x} and \texttt{print x,} - \end{block} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Basic looping} - \begin{lstlisting} -# Fibonacci series: -# the sum of two elements -# defines the next -a, b = 0, 1 -while b < 10: - print b, - a, b = b, a + b - -\end{lstlisting} -\typ{1 1 2 3 5 8}\\ -\alert{Recall it is easy to write infinite loops with \kwrd{while}} - \inctime{20} -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 20 m, running 80m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - +\subsection{Exercises on Control flow} \begin{frame} \frametitle{Problem set 1} \begin{itemize} @@ -630,7 +129,7 @@ \begin{frame}{Problem 1.2 - Collatz sequence} \begin{enumerate} \item Start with an arbitrary (positive) integer. - \item If the number is even, divide by 2; if the number is odd multiply by 3 and add 1. + \item If the number is even, divide by 2; if the number is odd, multiply by 3 and add 1. \item Repeat the procedure with the new number. \item It appears that for all starting values there is a cycle of 4, 2, 1 at which the procedure loops. \end{enumerate} @@ -660,11 +159,11 @@ The number of lines must be obtained from the user as input.\\ \pause When can your code fail? -\only<2->{\inctime{25}} +\only<2->{\inctime{20}} \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 25 m, running 105m +% TIME: 20 m, running 20m %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \subsection{Functions} @@ -750,10 +249,10 @@ \item Refer here: \url{http://docs.python.org/library/functions.html} \end{itemize} - \inctime{15} + \inctime{10} \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 15 m, running 120m +% TIME: 10 m, running 30m %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{frame}{Problem set 2} @@ -782,11 +281,11 @@ A pair of numbers (a, b) is said to be \alert{amicable} if the aliquot number of a is b and the aliquot number of b is a.\\ Example: \texttt{220, 284}\\ Write a program that prints all five digit amicable pairs. - \inctime{30} + \inctime{25} \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 30 m, running 150m +% TIME: 25 m, running 55m %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \subsection{Lists} @@ -818,7 +317,7 @@ >>> a[1:3] # A slice. [2, 3] >>> a[1:-1] -[2, 3, 4] +[2, 3] >>> a[1:] == a[1:-1] False \end{lstlisting} @@ -843,7 +342,7 @@ \begin{lstlisting} >>> a = [1, 2, 3, 4] >>> a[:2] -[1, 3] +[1, 2] >>> a[0:-1:2] [1, 3] \end{lstlisting} @@ -871,8 +370,13 @@ >>> a [123, 1234, 12345] \end{lstlisting} +\inctime{10} \end{frame} +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +% TIME: 10 m, running 65m +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + \begin{frame}[fragile] \frametitle{List methods} \begin{lstlisting} @@ -880,7 +384,7 @@ >>> a.reverse() # in situ >>> a [12, 1, 'eggs', 'spam'] ->>> a.append(['x', 1]) +>>> a.append(['x', 1]) >>> a [12, 1, 'eggs', 'spam', ['x', 1]] >>> a.extend([1,2]) # Extend the list. @@ -903,8 +407,13 @@ >>> 'ell' in 'hello world' True \end{lstlisting} + \inctime{5} \end{frame} +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +% TIME: 5 m, running 70m +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + \begin{frame}[fragile] \frametitle{Tuples: immutable} \begin{lstlisting} @@ -914,15 +423,18 @@ >>> t[0] = 1 Traceback (most recent call last): File "", line 1, in ? -TypeError: object does not support item - assignment +TypeError: object does not support item assignment \end{lstlisting} \begin{itemize} \item Multiple return values are actually a tuple. \item Exchange is tuple (un)packing \end{itemize} +\inctime{5} +\end{frame} -\end{frame} +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +% TIME: 5 m, running 75m +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{frame}[fragile] \frametitle{\typ{range()} function} @@ -983,1763 +495,17 @@ 2 c \end{lstlisting} Try: \typ{print enumerate(a)} -\inctime{20} -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 20 m, running 170m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -\begin{frame} - {Problem set 3} - As you can guess, idea is to use \kwrd{for}! -\end{frame} - -\begin{frame}{Problem 3.1} - Which of the earlier problems is simpler when we use \kwrd{for} instead of \kwrd{while}? -\end{frame} - -\begin{frame}{Problem 3.2} - Given an empty chessboard and one Bishop placed in any square, say (r, c), generate the list of all squares the Bishop could move to. -\end{frame} - -\begin{frame}[fragile] - \frametitle{Problem 3.3} - - Given two real numbers \typ{a, b}, and an integer \typ{N}, write a - function named \typ{linspace( a, b, N)} that returns an ordered list - of \typ{N} points starting with \typ{a} and ending in \typ{b} and - equally spaced.\\ - - For example, \typ{linspace(0, 5, 11)}, should return, \\ -\begin{lstlisting} -[ 0.0 , 0.5, 1.0 , 1.5, 2.0 , 2.5, - 3.0 , 3.5, 4.0 , 4.5, 5.0 ] -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Problem 3.4a (optional)} - -Use the \typ{linspace} function and generate a list of N tuples of the form\\ -\typ{[($x_1$,f($x_1$)),($x_2$,f($x_2$)),\ldots,($x_N$,f($x_N$))]}\\for the following functions,\begin{itemize} - \item \typ{f(x) = sin(x)} - \item \typ{f(x) = sin(x) + sin(10*x)}. -\end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Problem 3.4b (optional)} - - Using the tuples generated earlier, determine the intervals where the roots of the functions lie. - - \inctime{15} +\inctime{10} \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 15 m, running 185m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -\subsection{IO} - -\begin{frame}[fragile] - \frametitle{Simple tokenizing and parsing} - \begin{lstlisting} -s = """The quick brown fox jumped - over the lazy dog""" -for word in s.split(): - print word.capitalize() - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Problem 4.1} - Given a string like, ``1, 3-7, 12, 15, 18-21'', produce the list \\ - \begin{lstlisting} - [1,3,4,5,6,7,12,15,18,19,20,21] - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{File handling} -\begin{lstlisting} ->>> f = open('/path/to/file_name') ->>> data = f.read() # Read entire file. ->>> line = f.readline() # Read one line. ->>> f.close() # close the file. -\end{lstlisting} -Writing files -\begin{lstlisting} ->>> f = open('/path/to/file_name', 'w') ->>> f.write('hello world\n') ->>> f.close() -\end{lstlisting} -\begin{itemize} - \item Everything read or written is a string -\end{itemize} -\emphbar{Try \typ{file?} for more help} -\end{frame} - -\begin{frame}[fragile] - \frametitle{File and \kwrd{for}} -\begin{lstlisting} ->>> f = open('/path/to/file_name') ->>> for line in f: -... print line -... -\end{lstlisting} -\end{frame} - -\begin{frame}{Problem 4.2} - The given file has lakhs of records in the form:\\ - \typ{RGN;ID;NAME;MARK1;\ldots;MARK5;TOTAL;PFW}\\ - Some entries may be empty. Read the data from this file and print the - name of the student with the maximum total marks. -\end{frame} - -\begin{frame}{Problem 4.3} - For the same data file compute the average marks in different - subjects, the student with the maximum mark in each subject and also - the standard deviation of the marks. Do this efficiently. - - \inctime{20} -\end{frame} - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 20 m, running 205m -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -\subsection{Modules} - -\begin{frame}[fragile] - {Modules} -\begin{lstlisting} ->>> sqrt(2) -Traceback (most recent call last): - File "", line 1, in -NameError: name 'sqrt' is not defined ->>> import math ->>> math.sqrt(2) -1.4142135623730951 -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - {Modules} - \begin{itemize} - \item The \kwrd{import} keyword ``loads'' a module - \item One can also use: - \begin{lstlisting} ->>> from math import sqrt ->>> from math import * - \end{lstlisting} - \item What is the difference? - \item \alert{Use the later only in interactive mode} - \end{itemize} - \emphbar{Package hierarchies} - \begin{lstlisting} ->>> from os.path import exists - \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} -\end{frame} - -\begin{frame}[fragile] - {Modules of special interest} - \begin{description}[matplotlibfor2d] - - \item[\typ{numpy}] Efficient, powerful numeric arrays - - \item[\typ{matplotlib}] Easy, interactive, 2D plotting - - \item[\typ{scipy}] statistics, optimization, integration, linear - algebra, Fourier transforms, signal and image processing, - genetic algorithms, ODE solvers, special functions, and more - - \item[Mayavi] Easy, interactive, 3D plotting - - \end{description} -\end{frame} - -\begin{frame}[fragile] - {Creating your own modules} - \begin{itemize} - \item Define variables, functions and classes in a file with a - \typ{.py} extension - \item This file becomes a module! - \item Accessible when in the current directory - \item Use \typ{cd} in IPython to change directory - - \item Naming your module - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Modules: example} - \begin{lstlisting} -# --- arith.py --- -def gcd(a, b): - if a%b == 0: return b - return gcd(b, a%b) -def lcm(a, b): - return a*b/gcd(a, b) -# ------------------ ->>> import arith ->>> arith.gcd(26, 65) -13 ->>> arith.lcm(26, 65) -130 - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Problem 5.1} - - Put all the functions you have written so far as part of the problems - into one module called \typ{iitb.py} and use this module from IPython. - -\inctime{20} -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -% TIME: 20 m, running 225m +% TIME: 10 m, running 85m %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{frame} \frametitle{Did we meet the goal?} \tableofcontents % You might wish to add the option [pausesections] - \end{frame} - - \begin{frame} - {Tomorrow} - \begin{itemize} - \item Plotting: 2D, 3D - \item NumPy, SciPy - \item Dictionary, Set - \item Debugging - \item Testing - \item \ldots - \end{itemize} - 11:30--13:00 Discussion of answers to problems OPTIONAL - \end{frame} -\end{document} - - -\begin{frame}[fragile] - \frametitle{More on functions} - \begin{itemize} - \item Support default and keyword arguments - \item Scope of variables in the function is local - \item Mutable items are \alert{passed by reference} - \item First line after definition may be a documentation string - (\alert{recommended!}) - \item Function definition and execution defines a name bound to the - function - \item You \emph{can} assign a variable to a function! - \end{itemize} -\end{frame} - - -\begin{frame}[fragile] - \frametitle{Functions: default arguments} - \begin{lstlisting} -def ask_ok(prompt, retries=4, 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 - retries = retries - 1 - if retries < 0: - raise IOError, 'bad user' - print complaint - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Functions: keyword arguments} - \begin{lstlisting} -def parrot(voltage, state='a stiff', - action='voom', type='Norwegian Blue'): - print "-- This parrot wouldn't", action, - print "if you put", voltage, "Volts through it." - print "-- Lovely plumage, the", type - print "-- It's", state, "!" - -parrot(1000) -parrot(action = 'VOOOOOM', voltage = 1000000) -parrot('a thousand', state = 'pushing up the daisies') -parrot('a million', 'bereft of life', 'jump') -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Functions: arbitrary argument lists} - \begin{itemize} - \item Arbitrary number of arguments using \verb+*args+ or - \verb+*whatever+ - \item Keyword arguments using \verb+**kw+ - \item Given a tuple/dict how do you call a function? - \begin{itemize} - \item Using argument unpacking - \item For positional arguments: \verb+foo(*[5, 10])+ - \item For keyword args: \verb+foo(**{'a':5, 'b':10})+ - \end{itemize} - \end{itemize} -\begin{lstlisting} -def foo(a=10, b=100): - print a, b -def func(*args, **keyword): - print args, keyword -# Unpacking: -args = [5, 10] -foo(*args) -kw = {'a':5, 'b':10} -foo(**kw) -\end{lstlisting} -\end{frame} - -\subsection{Modules, exceptions, classes} - -\begin{frame} - \frametitle{Modules} - \begin{itemize} - \item Define variables, functions and classes in a file with a - \typ{.py} extension - \item This file becomes a module! - \item Modules are searched in the following: - \begin{itemize} - \item Current directory - \item Standard: \typ{/usr/lib/python2.3/site-packages/} etc. - \item Directories specified in PYTHONPATH - \item \typ{sys.path}: current path settings (from the \typ{sys} - module) - \end{itemize} - \item The \typ{import} keyword ``loads'' a module - \item One can also use: - \mbox{\typ{from module import name1, name2, name2}}\\ - where \typ{name1} etc. are names in the module, ``module'' - \item \typ{from module import *} \ --- imports everything from module, - \alert{use only in interactive mode} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Modules: example} - \begin{lstlisting} -# --- foo.py --- -some_var = 1 -def fib(n): # write Fibonacci series up to n - """Print a Fibonacci series up to n.""" - a, b = 0, 1 - while b < n: - print b, - a, b = b, a+b -# EOF - ->>> import foo ->>> foo.fib(10) -1 1 2 3 5 8 ->>> foo.some_var -1 - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Namespaces} - \begin{itemize} - \item A mapping from names to objects - \item Modules introduce a namespace - \item So do classes - \item The running script's namespace is \verb+__main__+ - \item A modules namespace is identified by its name - \item The standard functions (like \typ{len}) are in the - \verb+__builtin__+ namespace - \item Namespaces help organize different names and their bindings to - different objects - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{Exceptions} - \begin{itemize} - \item Python's way of notifying you of errors - \item Several standard exceptions: \typ{SyntaxError}, \typ{IOError} - etc. - \item Users can also \typ{raise} errors - \item Users can create their own exceptions - \item Exceptions can be ``caught'' via \typ{try/except} blocks - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Exception: examples} -\begin{lstlisting} ->>> 10 * (1/0) -Traceback (most recent call last): - File "", line 1, in ? -ZeroDivisionError: integer division or modulo by zero ->>> 4 + spam*3 -Traceback (most recent call last): - File "", line 1, in ? -NameError: name 'spam' is not defined ->>> '2' + 2 -Traceback (most recent call last): - File "", line 1, in ? -TypeError: cannot concatenate 'str' and 'int' objects -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Exception: examples} -\begin{lstlisting} ->>> while True: -... try: -... x = int(raw_input("Enter a number: ")) -... break -... except ValueError: -... print "Invalid number, try again..." -... ->>> # To raise exceptions -... raise ValueError, "your error message" -Traceback (most recent call last): - File "", line 2, in ? -ValueError: your error message -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes: the big picture} - \begin{itemize} - \item Lets you create new data types - \item Class is a template for an object belonging to that class - \item Note: in Python a class is also an object - \item Instantiating a class creates an instance (an object) - \item An instance encapsulates the state (data) and behavior - (methods) - \item Allows you to define an inheritance hierarchy - \begin{itemize} - \item ``A Honda car \alert{is a} car.'' - \item ``A car \alert{is an} automobile.'' - \item ``A Python \alert{is a} reptile.'' - \end{itemize} - \item Programmers need to think OO - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes: what's the big deal?} - \begin{itemize} - \item Lets you create objects that mimic a real problem being - simulated - \item Makes problem solving more natural and elegant - \item Easier to create code - \item Allows for code-reuse - \item Polymorphism - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Class definition and instantiation} - \begin{itemize} - \item Class definitions when executed create class objects - \item Instantiating the class object creates an instance of the - class - \end{itemize} -\footnotesize -\begin{lstlisting} -class Foo(object): - pass -# class object created. -# Create an instance of Foo. -f = Foo() -# Can assign an attribute to the instance -f.a = 100 -print f.a -100 -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes \ldots} - \begin{itemize} - \item All attributes are accessed via the \typ{object.attribute} - syntax - \item Both class and instance attributes are supported - \item \emph{Methods} represent the behavior of an object: crudely - think of them as functions ``belonging'' to the object - \item All methods in Python are ``virtual'' - \item Inheritance through subclassing - \item Multiple inheritance is supported - \item No special public and private attributes: only good - conventions - \begin{itemize} - \item \verb+object.public()+: public - \item \verb+object._private()+ \& \verb+object.__priv()+: - non-public - \end{itemize} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes: examples} -\begin{lstlisting} -class MyClass(object): - """Example class (this is the class docstring).""" - i = 12345 # A class attribute - def f(self): - """This is the method docstring""" - return 'hello world' - ->>> a = MyClass() # creates an instance ->>> a.f() -'hello world' ->>> # a.f() is equivalent to MyClass.f(a) -... # This also explains why f has a 'self' argument. -... MyClass.f(a) -'hello world' -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes (continued)} - \begin{itemize} - \item \typ{self} is \alert{conventionally} the first argument for a - method - \item In previous example, \typ{a.f} is a method object - \item When \typ{a.f} is called, it is passed the instance \typ{a} as - the first argument - \item If a method called \verb+__init__+ exists, it is called when - the object is created - \item If a method called \verb+__del__+ exists, it is called before - the object is garbage collected - \item Instance attributes are set by simply ``setting'' them in - \typ{self} - \item Other special methods (by convention) like \verb+__add__+ let - you define numeric types: - {\footnotesize \url{http://docs.python.org/ref/specialnames.html} - \\ \url{http://docs.python.org/ref/numeric-types.html} - } - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes: examples} -\begin{lstlisting} -class Bag(MyClass): # Shows how to derive classes - def __init__(self): # called on object creation. - self.data = [] # an instance attribute - def add(self, x): - self.data.append(x) - def addtwice(self, x): - self.add(x) - self.add(x) ->>> a = Bag() ->>> a.f() # Inherited method -'hello world' ->>> a.add(1); a.addtwice(2) ->>> a.data -[1, 2, 2] -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Derived classes} - \begin{itemize} - \item Call the parent's \verb+__init__+ if needed - \item If you don't need a new constructor, no need to define it in subclass - \item Can also use the \verb+super+ built-in function - \end{itemize} -\begin{lstlisting} -class AnotherBag(Bag): - def __init__(self): - # Must call parent's __init__ explicitly - Bag.__init__(self) - # Alternatively use this: - super(AnotherBag, self).__init__() - # Now setup any more data. - self.more_data = [] -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Classes: polymorphism} -\begin{lstlisting} -class Drawable(object): - def draw(self): - # Just a specification. - pass -\end{lstlisting} -\mode{\pause} -\begin{lstlisting} -class Square(Drawable): - def draw(self): - # draw a square. -class Circle(Drawable): - def draw(self): - # draw a circle. -\end{lstlisting} -\mode{\pause} -\begin{lstlisting} -class Artist(Drawable): - def draw(self): - for obj in self.drawables: - obj.draw() -\end{lstlisting} -\end{frame} - -\subsection{Miscellaneous} - -\begin{frame}[fragile] - \frametitle{Stand-alone scripts} -Consider a file \typ{f.py}: -\begin{lstlisting} -#!/usr/bin/env python -"""Module level documentation.""" -# First line tells the shell that it should use Python -# to interpret the code in the file. -def f(): - print "f" - -# Check if we are running standalone or as module. -# When imported, __name__ will not be '__main__' -if __name__ == '__main__': - # This is not executed when f.py is imported. - f() -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{List comprehensions} -\begin{lstlisting} ->>> veg = ['tomato', 'cabbage', 'carrot', 'potato'] ->>> [x.upper() for x in veg] -['TOMATO', 'CABBAGE', 'CARROT', 'POTATO'] ->>> vec = range(0, 8) ->>> even = [x for x in vec if x%2 == 0] ->>> even -[0, 2, 4, 6] ->>> [x*x for x in even] -[0, 4, 16, 36] ->>> odd = [x for x in vec if x%2 == 1] ->>> odd -[1, 3, 5, 7] ->>> [x*y for x in even for y in odd] -[0, 0, 0, 0, 2, 6, 10, 14, 4, 12, 20, 28, 6, 18,30,42] -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{More IPython features} - \begin{itemize} - \item Input and output caching: - \begin{itemize} - \item \verb+In+: a list of all entered input - \item \verb+Out+: a dict of all output - \item \verb+_+, \verb+__+, \verb+__+ are the last three results as - is \verb+_N+ - \item \verb+%hist [-n]+ macro shows previous history, \verb+-n+ - suppresses line number information - \end{itemize} - \item Log the session using \verb+%logstart+, \verb+%logon+ and - \verb+%logoff+ - \item \verb+%run [options] file[.py]+ -- running Python code - \begin{itemize} - \item \verb+%run -d [-b]+: debug script with pdb - \verb+N+ is the line number to break at (defaults to 1) - \item \verb+%run -t+: time the script - \item \verb+%run -p+: Profile the script - \end{itemize} - \item \verb+%prun+ runs a statement/expression under the profiler - \item \verb+%macro [options] macro_name n1-n2 n3-n4 n6+ save specified - lines to a macro with name \verb+macro_name+ - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{More IPython features \ldots} - \begin{itemize} - \item \verb+%edit [options] [args]+: edit lines of code or file - specified in editor (configure editor via \verb+$EDITOR+) - \item \verb+%cd+ changes directory, see also \verb+%pushd, %popd, %dhist+ - \item Shell access - \begin{itemize} - \item \verb+!command+ runs a shell command and returns its output - \item \verb+files = %sx ls+ or \verb+files = !ls+ sets - \verb+files+ to all result of the \verb+ls+ command - \item \verb+%sx+ is quiet - \item \verb+!ls $files+ passes the \verb+files+ variable to the - shell command - \item \verb+%alias alias_name cmd+ creates an alias for a system - command - \end{itemize} - \item \verb+%colors+ lets you change the color scheme to - \verb+NoColor, Linux, LightBG+ - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{More IPython features \ldots} - \begin{itemize} - \item Use \verb+;+ at the end of a statement to suppress printing - output - \item \verb+%bookmark+: store a bookmarked location, for use with \verb+%cd+ - \item \verb+%who, %whos+: print information on variables - \item \verb+%save [options] filename n1-n2 n3-n4+: save lines to a - file - \item \verb+%time statement+: Time execution of a Python statement or - expression - \item \verb+%timeit [-n -r [-t|-c]] statement+: time execution - using Python's timeit module - \item Can define and use profiles to setup IPython differently: - \verb+math, scipy, numeric, pysh+ etc. - \item \verb+%magic+: \alert{Show help on all magics} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{File handling} -\begin{lstlisting} ->>> # Reading files: -... f = open('/path/to/file_name') ->>> data = f.read() # Read entire file. ->>> line = f.readline() # Read one line. ->>> # Read entire file appending each line into a list -... lines = f.readlines() ->>> f.close() # close the file. ->>> # Writing files: -... f = open('/path/to/file_name', 'w') ->>> f.write('hello world\n') -\end{lstlisting} - \begin{itemize} - \item \typ{tell()}: returns int of current position - \item \typ{seek(pos)}: moves current position to specified byte - \item Call \typ{close()} when done using a file - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Math} - \begin{itemize} - \item \typ{math} module provides basic math routines for - floats - \item \typ{cmath} module provides math routies for complex - numbers - \item \typ{random}: provides pseudo-random number generators - for various distributions - \item These are always available and part of the standard library - \item More serious math is provided by the NumPy/SciPy modules -- - these are not standard and need to be installed separately - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Timing and profiling} - \begin{itemize} - \item Timing code: use the \typ{time} module - \item Read up on \typ{time.time()} and \typ{time.clock()} - \item \typ{timeit}: is a better way of doing timing - \item IPython has handy \typ{time} and \typ{timeit} macros (type - \typ{timeit?} for help) - \item IPython lets you debug and profile code via the \typ{run} - macro (type \typ{run?} on the prompt to learn more) - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Odds and ends} - \begin{itemize} - \item \typ{dir([object])} function: attributes of given object - \item \typ{type(object)}: returns type information - \item \typ{str(), repr()}: convert object to string representation - \item \typ{isinstance, issubclass} - \item \typ{assert} statements let you do debugging assertions in - code - \item \typ{csv} module: reading and writing CSV files - \item \typ{pickle}: lets you save and load Python objects - (\alert{serialization}) - \item \typ{sys.argv}: command line arguments - \item \typ{os.path}: common path manipulations - \item Check out the Python Library reference: - \url{http://docs.python.org/lib/lib.html} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Test driven development (TDD)} - \begin{itemize} - \item Why? - \begin{itemize} - - \item Forces you to write reusable code! - - \item Think about the API - - \item More robust - - \item Makes refactoring very easy - - \end{itemize} - \item How? Python offers three major ways of doing this - \begin{itemize} - \item doctest - \item unittest - \item nosetest (and similar like py.test) - \end{itemize} - - \item Test every piece of functionality you offer - - \item This isn't a formal introduction but more a practical one - - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Unit test} -\begin{lstlisting} -import unittest - -class MyTestCase(unittest.TestCase): - def setUp(self): - # Called *before* each test_* - def tearDown(self): - # Called *after* each test_* - def test_something(self): - "docstring" - # Test code. - self.assertEqual(x, y) - self.assertRaises(ValueError, func, arg1, arg2 ...) - -if __name__ == '__main__': - unittest.main() -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Nosetest} -\begin{lstlisting} -import particle -def test_particle(): - # Use asserts here. - p = particle.Particle(1.0) - assert p.property[0] == 1.0 - assert p.property[2] == 0.0 - -if __name__ == '__main__': - import nose - nose.main() -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Testing} - \begin{itemize} - \item More details: see library reference and search for nosetest - \end{itemize} -\end{frame} - -\section{Numerics \& Plotting} - -\subsection{NumPy Arrays} - -\newcommand{\num}{\texttt{numpy}} - -\begin{frame} - \frametitle{The \num\ module} - \begin{itemize} - \item Manipulating large Python lists for scientific computing is - \alert{slow} - \item Most complex computations can be reduced to a few standard - operations - \item The \num\ module provides: - \begin{itemize} - \item An efficient and powerful array type for various common data - types - \item Abstracts out the most commonly used standard operations on - arrays - \end{itemize} - \item Numeric was the first, then came \texttt{numarray}. - \texttt{numpy} is the latest and is the future - \item This course uses \num\ and only covers the absolute basics - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{Basic concepts} - \begin{itemize} - \item \num\ arrays are of a fixed size (\typ{arr.size}) and have the - same type (\typ{arr.dtype}) - \item \num\ arrays may have arbitrary dimensionality - \item The \typ{shape} of an array is the extent (length) of the - array along each dimension - \item The \typ{rank(arr)} of an array is the ``dimensionality'' of the - array - \item The \typ{arr.itemsize} is the number of bytes (8-bits) used for - each element of the array - \item \alert{Note:} The \typ{shape} and \typ{rank} may change as - long as the \typ{size} of the array is fixed - \item \alert{Note:} \typ{len(arr) != arr.size} in general - \item \alert{Note:} By default array operations are performed - \alert{elementwise} - \item Indices start from 0 - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Examples of \num} -\begin{lstlisting} -# Simple array math example ->>> from numpy import * ->>> a = array([1,2,3,4]) ->>> b = array([2,3,4,5]) ->>> a + b # Element wise addition! -array([3, 5, 7, 9]) - ->>> print pi, e # Pi and e are defined. -3.14159265359 2.71828182846 -# Create array from 0 to 10 ->>> x = arange(0.0, 10.0, 0.05) ->>> x *= 2*pi/10 # multiply array by scalar value -array([ 0.,0.0314,...,6.252]) -# apply functions to array. ->>> y = sin(x) -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{More examples of \num} -\vspace*{-8pt} -\begin{lstlisting} -# Size, shape, rank, type etc. ->>> x = array([1., 2, 3, 4]) ->>> size(x) -4 ->>> x.dtype # or x.dtype.char -'d' ->>> x.shape -(4,) ->>> print rank(x), x.itemsize -1 8 ->>> x.tolist() -[1.0, 2.0, 3.0, 4.0] -# Array indexing ->>> x[0] = 10 ->>> print x[0], x[-1] -10.0 4.0 -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Multi-dimensional arrays} -\begin{lstlisting} ->>> a = array([[ 0, 1, 2, 3], -... [10,11,12,13]]) ->>> a.shape # (rows, columns) -(2, 4) -# Accessing and setting values ->>> a[1,3] -13 ->>> a[1,3] = -1 ->>> a[1] # The second row -array([10,11,12,-1]) - -# Flatten/ravel arrays to 1D arrays ->>> a.flat # or ravel(a) -array([0,1,2,3,10,11,12,-1]) -# Note: flat references original memory -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Slicing arrays} -\begin{lstlisting} ->>> a = array([[1,2,3], [4,5,6], [7,8,9]]) ->>> a[0,1:3] -array([2, 3]) ->>> a[1:,1:] -array([[5, 6], - [8, 9]]) ->>> a[:,2] -array([3, 6, 9]) -# Striding... ->>> a[0::2,0::2] -array([[1, 3], - [7, 9]]) -# All these slices are references to the same memory! -\end{lstlisting} -\end{frame} - -% \begin{frame}[fragile] -% \frametitle{Array types and typecodes} -% \begin{tabular}[c]{|c|c|p{2.75in}|} -% \hline -% Character & Bits (bytes) & Type name \\ -% \hline -% D & 128 (16) & \typ{Complex, Complex64}\\ -% F & 64 (8) & \typ{Complex0, Complex8, Complex16} \\ -% d & 64 (8) & \typ{Float, Float64} \\ -% f & 32 (4) & \typ{Float0, Float8, Float16} \\ -% i & 32 (4) & \typ{Int32} \\ -% l & 32 (4) & \typ{Int} \\ -% O & 4 (1) & \typ{PyObject} \\ -% %b 8 (1) UnsignedInt8 -% %1 (one) 8 (1) Int8 -% %s 16 (2) Int16 -% \hline -% \end{tabular} -% \begin{lstlisting} -% # Examples -% >>> f = array([1,2,3], Float32) -% >>> c = array([1,2,3], Complex32) -% >>> print f, c -% [ 1. 2. 3.] [ 1.+0.j 2.+0.j 3.+0.j] -% \end{lstlisting} -% \end{frame} - -\begin{frame}[fragile] - \frametitle{Array creation functions} - \begin{itemize} - \item \typ{array(object, dtype=None, copy=1,order=None, subok=0,ndmin=0)} - \item \typ{arange(start, stop=None, step=1, dtype=None)} - \item \typ{linspace(start, stop, num=50, endpoint=True, retstep=False)} - \item \typ{ones(shape, dtype=None, order='C')} - \item \typ{zeros((d1,...,dn),dtype=float,order='C')} - \item \typ{identity(n)} - \item \typ{empty((d1,...,dn),dtype=float,order='C')} - \item \typ{ones\_like(x)}, \typ{zeros\_like(x)}, \typ{empty\_like(x)} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Array math} - \begin{itemize} - \item Basic \alert{elementwise} math (given two arrays \typ{a, b}): - \begin{itemize} - \item \typ{a + b $\rightarrow$ add(a, b)} - \item \typ{a - b, $\rightarrow$ subtract(a, b)} - \item \typ{a * b, $\rightarrow$ multiply(a, b)} - \item \typ{a / b, $\rightarrow$ divide(a, b)} - \item \typ{a \% b, $\rightarrow$ remainder(a, b)} - \item \typ{a ** b, $\rightarrow$ power(a, b)} - \end{itemize} - \item Inplace operators: \typ{a += b}, or \typ{add(a, b, - a)} etc. - \item Logical operations: \typ{equal (==)}, \typ{not\_equal (!=)}, - \typ{less (<)}, \typ{greater (>)} etc. - \item Trig and other functions: \typ{sin(x), arcsin(x), sinh(x), - exp(x), sqrt(x)} etc. - \item \typ{sum(x, axis=0), product(x, axis=0)}: sum and product of array elements - \item \typ{dot(a, b)} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Advanced} - \begin{itemize} - \item Only scratched the surface of \num - \item Ufunc methods: \typ{reduce, accumulate, outer, reduceat} - \item Typecasting - \item More functions: \typ{take, choose, where, compress, - concatenate} - \item Array broadcasting and \typ{None} - \end{itemize} -\end{frame} - -\subsection{Plotting: Matplotlib} - -\begin{frame} - \frametitle{About \texttt{matplotlib}} - \begin{itemize} - \item Easy to use, scriptable, ``Matlab-like'' 2D plotting - \item Publication quality figures and interactive capabilities - \item Plots, histograms, power spectra, bar charts, errorcharts, - scatterplots, etc. - \item Also does polar plots, maps, contours - \item Support for simple \TeX\ markup - \item Multiple output backends (images, EPS, SVG, wx, Agg, Tk, GTK) - \item Cross-platform: Linux, Win32, Mac OS X - \item Good idea to use via IPython: \typ{ipython -pylab} - \item From scripts use: \typ{import pylab} - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{More information} - \begin{itemize} - \item More information here: \url{http://matplotlib.sf.net} - \item \url{http://matplotlib.sf.net/tutorial.html} - \item \url{http://matplotlib.sf.net/screenshots.html} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Basic plotting with \texttt{matplotlib}} -\begin{lstlisting} ->>> x = arange(0, 2*pi, 0.05) ->>> plot(x, sin(x)) # Same as plot(x, sin(x), 'b-') ->>> plot(x, sin(x), 'ro') ->>> axis([0,2*pi, -1,1]) ->>> xlabel(r'$\chi$', color='g') ->>> ylabel(r'sin($\chi$)', color='r') ->>> title('A simple figure', fontsize=20) ->>> savefig('/tmp/test.eps') -# Multiple plots in one figure ->>> t = arange(0.0, 5.2, 0.2) -# red dashes, blue squares and green triangles ->>> plot(t, t, 'r--', t, t**2, 'bs', t, t**3, 'g^') -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Basic plotting \ldots} -\begin{lstlisting} -# Set properties of objects: ->>> plot(x, sin(x), linewidth=2.0, color='r') ->>> l, = plot(x, sin(x)) ->>> setp(l, linewidth=2.0, color='r') ->>> l.set_linewidth(2.0); l.set_color('r') ->>> draw() # Redraws current figure. ->>> setp(l) # Prints available properties ->>> close() # Closes the figure. -# Multiple figures: ->>> figure(1); plot(x, sin(x)) ->>> figure(2); plot(x, tanh(x)) ->>> figure(1); title('Easy as 1,2,3') -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Basic plotting \ldots} -\begin{lstlisting} ->>> figure(1) ->>> subplot(211) # Same as subplot(2, 1, 1) ->>> plot(x, cos(5*x)*exp(-x)) ->>> subplot(2, 1, 2) ->>> plot(x, cos(5*x), 'r--', label='cosine') ->>> plot(x, sin(5*x), 'g--', label='sine') ->>> legend() # Or legend(['cosine', 'sine']) ->>> text(1,0, '(1,0)') ->>> axes = gca() # Current axis ->>> fig = gcf() # Current figure -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{X-Y plot} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/xyplot} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -t1 = arange(0.0, 5.0, 0.1) -t2 = arange(0.0, 5.0, 0.02) -t3 = arange(0.0, 2.0, 0.01) -subplot(211) -plot(t1, cos(2*pi*t1)*exp(-t1), 'bo', - t2, cos(2*pi*t2)*exp(-t2), 'k') -grid(True) -title('A tale of 2 subplots') -ylabel('Damped') -subplot(212) -plot(t3, cos(2*pi*t3), 'r--') -grid(True) -xlabel('time (s)') -ylabel('Undamped') -\end{lstlisting} - \end{block} - \end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Errorbar} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/errorbar} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -t = arange(0.1, 4, 0.1) -s = exp(-t) -e = 0.1*abs(randn(len(s))) -f = 0.1*abs(randn(len(s))) -g = 2*e -h = 2*f -errorbar(t, s, [e,g], f, fmt='o') -xlabel('Distance (m)') -ylabel('Height (m)') -title('Mean and standard error '\ - 'as a function of distance') -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Semi-log and log-log plots} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/log} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -dt = 0.01 -t = arange(dt, 20.0, dt) -subplot(311) -semilogy(t, exp(-t/5.0)) -ylabel('semilogy') -grid(True) -subplot(312) -semilogx(t, sin(2*pi*t)) -ylabel('semilogx') -grid(True) -# minor grid on too -gca().xaxis.grid(True, which='minor') -subplot(313) -loglog(t, 20*exp(-t/10.0), basex=4) -grid(True) -ylabel('loglog base 4 on x') -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Histogram} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/histogram} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -mu, sigma = 100, 15 -x = mu + sigma*randn(10000) -# the histogram of the data -n, bins, patches = hist(x, 100, normed=1) -# add a 'best fit' line -y = normpdf( bins, mu, sigma) -l = plot(bins, y, 'r--', linewidth=2) -xlim(40, 160) -xlabel('Smarts') -ylabel('P') -title(r'$\rm{IQ:}\/ \mu=100,\/ \sigma=15$') -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Bar charts} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/barchart} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -N = 5 -menMeans = (20, 35, 30, 35, 27) -menStd = ( 2, 3, 4, 1, 2) -# the x locations for the groups -ind = arange(N) -# the width of the bars -width = 0.35 -p1 = bar(ind, menMeans, width, - color='r', yerr=menStd) -womenMeans = (25, 32, 34, 20, 25) -womenStd = ( 3, 5, 2, 3, 3) -p2 = bar(ind+width, womenMeans, width, - color='y', yerr=womenStd) -ylabel('Scores') -title('Scores by group and gender') -xticks(ind+width, - ('G1', 'G2', 'G3', 'G4', 'G5')) -xlim(-width,len(ind)) -yticks(arange(0,41,10)) -legend((p1[0], p2[0]), - ('Men', 'Women'), shadow=True) -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Pie charts} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.4in} - \includegraphics[height=2.0in, interpolate=true]{data/piechart} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -# make a square figure and axes -figure(1, figsize=(8,8)) -ax = axes([0.1, 0.1, 0.8, 0.8]) -labels = 'Frogs', 'Hogs', 'Dogs', 'Logs' -fracs = [15,30,45, 10] -explode=(0, 0.05, 0, 0) -pie(fracs, explode=explode, labels=labels, - autopct='%1.1f%%', shadow=True) -title('Raining Hogs and Dogs', - bbox={'facecolor':'0.8', 'pad':5}) -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Scatter plots} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.4in} - \includegraphics[height=2in, interpolate=true]{data/scatter} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -N = 30 -x = 0.9*rand(N) -y = 0.9*rand(N) -# 0 to 10 point radiuses -area = pi*(10 * rand(N))**2 -volume = 400 + rand(N)*450 -scatter(x,y,s=area, marker='o', c=volume, - alpha=0.75) -xlabel(r'$\Delta_i$', size='x-large') -ylabel(r'$\Delta_{i+1}$', size='x-large') -title(r'Volume and percent change') -grid(True) -colorbar() -savefig('scatter') -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Polar} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/polar} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -figure(figsize=(8,8)) -ax = axes([0.1, 0.1, 0.8, 0.8], polar=True, - axisbg='#d5de9c') -r = arange(0,1,0.001) -theta = 2*2*pi*r -polar(theta, r, color='#ee8d18', lw=3) -# the radius of the grid labels -setp(ax.thetagridlabels, y=1.075) -title(r"$\theta=4\pi r", fontsize=20) -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Contours} - \begin{columns} - \column{0.45\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/contour} - \column{0.525\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -x = arange(-3.0, 3.0, 0.025) -y = arange(-2.0, 2.0, 0.025) -X, Y = meshgrid(x, y) -Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0) -Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1) -# difference of Gaussians -Z = 10.0 * (Z2 - Z1) -im = imshow(Z, interpolation='bilinear', - origin='lower', - cmap=cm.gray, extent=(-3,3,-2,2)) -levels = arange(-1.2, 1.6, 0.2) -# label every second level -clabel(CS, levels[1::2], inline=1, - fmt='%1.1f', fontsize=14) -CS = contour(Z, levels, - origin='lower', - linewidths=2, - extent=(-3,3,-2,2)) -# make a colorbar for the contour lines -CB = colorbar(CS, shrink=0.8, extend='both') -title('Lines with colorbar') -hot(); flag() -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Velocity vectors} - \begin{columns} - \column{0.5\textwidth} - \hspace*{-0.5in} - \includegraphics[height=2in, interpolate=true]{data/quiver} - \column{0.45\textwidth} - \begin{block}{Example code} - \tiny -\begin{lstlisting} -X,Y = meshgrid(arange(0,2*pi,.2), - arange(0,2*pi,.2) ) -U = cos(X) -V = sin(Y) -Q = quiver(X[::3, ::3], Y[::3, ::3], - U[::3, ::3], V[::3, ::3], - color='r', units='x', - linewidths=(2,), - edgecolors=('k'), - headaxislength=5 ) -qk = quiverkey(Q, 0.5, 0.03, 1, '1 m/s', - fontproperties= - {'weight': 'bold'}) -axis([-1, 7, -1, 7]) -title('triangular head; scale '\ - 'with x view; black edges') -\end{lstlisting} - \end{block} -\end{columns} -\end{frame} - -\begin{frame}[fragile] \frametitle{Maps} - \includegraphics[height=2.5in, interpolate=true]{data/plotmap} - \begin{center} - \tiny - For details see \url{http://matplotlib.sourceforge.net/screenshots/plotmap.py} - \end{center} -\end{frame} - - -\subsection{SciPy} - -\begin{frame} - \frametitle{Using \texttt{SciPy}} - \begin{itemize} - \item SciPy is Open Source software for mathematics, science, and - engineering - \item \typ{import scipy} - \item Built on NumPy - \item Provides modules for statistics, optimization, integration, - linear algebra, Fourier transforms, signal and image processing, - genetic algorithms, ODE solvers, special functions, and more - \item Used widely by scientists world over - \item Details are beyond the scope of this tutorial - \end{itemize} -\end{frame} - -\section{Standard library} - -\subsection{Quick Tour} - -\begin{frame} - \frametitle{Standard library} - \begin{itemize} - \item Very powerful - \item ``Batteries included'' - \item Example standard modules taken from the tutorial - \begin{itemize} - \item Operating system interface: \typ{os} - \item System, Command line arguments: \typ{sys} - \item Regular expressions: \typ{re} - \item Math: \typ{math}, \typ{random} - \item Internet access: \typ{urllib2}, \typ{smtplib} - \item Data compression: \typ{zlib}, \typ{gzip}, \typ{bz2}, - \typ{zipfile}, and \typ{tarfile} - \item Unit testing: \typ{doctest} and \typ{unittest} - \item And a whole lot more! - \end{itemize} - \item Check out the Python Library reference: - \url{http://docs.python.org/lib/lib.html} - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Stdlib: examples} -\begin{lstlisting} ->>> import os ->>> os.system('date') -Fri Jun 10 22:13:09 IST 2005 -0 ->>> os.getcwd() -'/home/prabhu' ->>> os.chdir('/tmp') ->>> import os ->>> dir(os) - ->>> help(os) - -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Stdlib: examples} -\begin{lstlisting} ->>> import sys ->>> # Print the list of command line args to Python -... print sys.argv -[''] ->>> import re # Regular expressions ->>> re.findall(r'\bf[a-z]*', -... 'which foot or hand fell fastest') -['foot', 'fell', 'fastest'] ->>> re.sub(r'(\b[a-z]+) \1', r'\1', -... 'cat in the the hat') -'cat in the hat' -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Stdlib: examples} -\begin{lstlisting} ->>> import math ->>> math.cos(math.pi / 4.0) -0.70710678118654757 ->>> math.log(1024, 2) -10.0 ->>> import random ->>> random.choice(['apple', 'pear', 'banana']) -'pear' -\end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Stdlib: examples} -\begin{lstlisting} ->>> import urllib2 ->>> f = urllib2.urlopen('http://www.python.org/') ->>> print f.read(100) - ->> import zlib ->>> s = 'witch which has which witches wrist watch' ->>> len(s) -41 ->>> t = zlib.compress(s) ->>> len(t) -37 ->>> zlib.decompress(t) -'witch which has which witches wrist watch' ->>> zlib.crc32(t) --1438085031 -\end{lstlisting} -\end{frame} - -\begin{frame} - \frametitle{Summary} - \begin{itemize} - \item Introduced Python - \item Basic syntax - \item Basic types and data structures - \item Control flow - \item Functions - \item Modules - \item Exceptions - \item Classes - \item Standard library - \end{itemize} \end{frame} \end{document} - -\subsection{Basic data structures} -\begin{frame}{Lists} - \begin{itemize} - \item \texttt{species = [ 'humans', 'orcs', 'elves', 'dwarves' ]} - \item \texttt{ ids = [ 107, 109, 124, 141, 142, 144 ]} - \item \texttt{ oneliners = [ 'I will be back', 'Do or do not! No try!!', 42 ] } - \end{itemize} - - \begin{block}{List operations} - ids + [ 100, 102 ]\\ - species.append( 'unicorns')\\ - print oneliners[ 1 ]\\ - look up \alert{docs.python.org/tutorial/datastructures.html} - \end{block} -\end{frame} -\end{document} -\section{Python Tutorial} -\subsection{Preliminaries} -\begin{frame} - \frametitle{Using the interpreter} - \begin{itemize} - \item Starting up: \typ{python} or \typ{ipython} - \item Quitting: \typ{Control-D} or \typ{Control-Z} (on Win32) - \item Can use it like a calculator - \item Can execute one-liners via the \typ{-c} option: - \typ{python -c "print 'hello world'"} - \item Other options via \typ{python -h} - \end{itemize} -\end{frame} - -\begin{frame} - \frametitle{IPython} - \begin{itemize} - \item Recommended interpreter, IPython: - \url{http://ipython.scipy.org} - \item Better than the default Python shell - \item Supports tab completion by default - \item Easier object introspection - \item Shell access! - \item Command system to allow extending its own behavior - \item Supports history (across sessions) and logging - \item Can be embedded in your own Python code - \item Support for macros - \item A flexible framework for your own custom interpreter - \item Other miscellaneous conveniences - \item We'll get back to this later - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Basic IPython features} - \begin{itemize} - \item Startup: \verb+ipython [options] files+ - \begin{itemize} - \item \verb+ipython [-wthread|-gthread|-qthread]+: - Threading modes to support wxPython, pyGTK and Qt - \item \verb+ipython -pylab+: Support for matplotlib - \end{itemize} - \item TAB completion: - \begin{itemize} - \item Type \verb+object_name.+ to see list of options - \item Also completes on file and directory names - \end{itemize} - \item \verb+object?+ shows docstring/help for any Python object - \item \verb+object??+ presents more docs (and source if possible) - \item Debugging with \verb+%pdb+ magic: pops up pdb on errors - \item Access history (saved over earlier sessions also) - \begin{itemize} - \item Use \texttt{}: move up history - \item Use \texttt{ string}: search history backwards - \item Use \texttt{Esc >}: get back to end of history - \end{itemize} - \item \verb+%run [options] file[.py]+ lets you run Python code - \end{itemize} -\end{frame} -% LocalWords: BDFL Guido Rossum PSF Nokia OO Zope CMS RedHat SciPy MayaVi spam -% LocalWords: IPython ipython stdin TypeError dict int elif PYTHONPATH IOError -% LocalWords: namespace Namespaces SyntaxError ZeroDivisionError NameError str -% LocalWords: ValueError subclassed def - - - \item Types are of two kinds: \alert{mutable} and \alert{immutable} - \item Immutable types: numbers, strings, \typ{None} and tuples - \item Immutables cannot be changed ``in-place'' - \item Mutable types: lists, dictionaries, instances, etc. - \item Mutable objects can be ``changed'' - \end{itemize} - - -\begin{frame} - \frametitle{Important!} - \begin{itemize} - \item Assignment to an object is by reference - \item Essentially, \alert{names are bound to objects} - \end{itemize} -\end{frame} - - -\end{document} -\begin{frame}[fragile] - \frametitle{Dictionaries} - \begin{itemize} - \item Associative arrays/mappings - \item Indexed by ``keys'' (keys must be immutable) - \item \typ{dict[key] = value} - \item \typ{keys()} returns all keys of the dict - \item \typ{values()} returns the values of the dict - \item \verb+has_key(key)+ returns if \typ{key} is in the dict - \end{itemize} -\end{frame} - -\begin{frame}[fragile] - \frametitle{Dictionaries: example} - \begin{lstlisting} ->>> tel = {'jack': 4098, 'sape': 4139} ->>> tel['guido'] = 4127 ->>> tel -{'sape': 4139, 'guido': 4127, 'jack': 4098} ->>> tel['jack'] -4098 ->>> del tel['sape'] ->>> tel['irv'] = 4127 ->>> tel -{'guido': 4127, 'irv': 4127, 'jack': 4098} ->>> tel.keys() -['guido', 'irv', 'jack'] ->>> tel.has_key('guido') -True - \end{lstlisting} -\end{frame} - -\subsection{Control flow, functions} - - - -\begin{frame}[fragile] - \frametitle{\typ{If} example} - \begin{lstlisting} ->>> a = ['cat', 'window', 'defenestrate'] ->>> if 'cat' in a: -... print "meaw" -... -meaw ->>> pets = {'cat': 1, 'dog':2, 'croc': 10} ->>> if 'croc' in pets: -... print pets['croc'] -... -10 - \end{lstlisting} -\end{frame} - -\begin{frame}[fragile] - \frametitle{\typ{for} example} - \begin{lstlisting} ->>> a = ['cat', 'window', 'defenestrate'] ->>> for x in a: -... print x, len(x) -... -cat 3 -window 6 -defenestrate 12 ->>> knights = {'gallahad': 'the pure', -... 'robin': 'the brave'} ->>> for k, v in knights.iteritems(): -... print k, v -... -gallahad the pure -robin the brave -\end{lstlisting} -\end{frame}