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diff --git a/day2/session2.tex b/day2/session2.tex index 7aadfc1..c20a2bb 100644 --- a/day2/session2.tex +++ b/day2/session2.tex @@ -1,8 +1,8 @@ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %Tutorial slides on Python. % -% Author: Prabhu Ramachandran <prabhu at aero.iitb.ac.in> -% Copyright (c) 2005-2009, Prabhu Ramachandran +% Author: FOSSEE +% Copyright (c) 2009, FOSSEE, IIT Bombay %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \documentclass[14pt,compress]{beamer} @@ -78,7 +78,7 @@ \author[FOSSEE Team] {The FOSSEE Group} \institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay} -\date[] {1, November 2009\\Day 2, Session 2} +\date[] {8 November, 2009\\Day 2, Session 2} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %\pgfdeclareimage[height=0.75cm]{iitmlogo}{iitmlogo} @@ -123,13 +123,113 @@ % You might wish to add the option [pausesections] \end{frame} +\section{Control flow} +\subsection{Basic Looping} +\begin{frame}[fragile] + \frametitle{\typ{while}} +Example: Fibonacci series + \begin{lstlisting} +# the sum of two elements +# defines the next +In []: a, b = 0, 1 +In []: while b < 10: + ...: print b, + ...: a, b = b, a + b + ...: + ...: +\end{lstlisting} +\typ{1 1 2 3 5 8}\\ +\end{frame} + +\begin{frame}[fragile] +\frametitle{\typ{range()}} +\kwrd{range([start,] stop[, step])}\\ +\begin{itemize} + \item range() returns a list of integers + \item The \emph{start} and the \emph{step} arguments are optional + \item \emph{stop} argument is not included in the list +\end{itemize} +\vspace*{.5in} +\begin{itemize} + \item \alert{Anything within \typ{[]} is optional} + \begin{itemize} + \item Nothing to do with Python. + \end{itemize} +\end{itemize} + +\end{frame} + +\begin{frame}[fragile] + \frametitle{\typ{for} \ldots \typ{range()}} +Example: print squares of first \typ{n} numbers + \begin{lstlisting} +In []: for i in range(5): + ....: print i, i * i + ....: + ....: +0 0 +1 1 +2 4 +3 9 +4 16 +\end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{\typ{for} \ldots \typ{range()}} +Example: print squares of odd numbers from 3 to 9 + \begin{lstlisting} +In []: for i in range(3, 10, 2): + ....: print i, i * i + ....: + ....: +3 9 +5 25 +7 49 +9 81 +\end{lstlisting} +\inctime{5} +\end{frame} + +\subsection{Exercises} + +\begin{frame}{Problem set 1: Problem 1.1} + Write a program that displays all three digit numbers that are equal to the sum of the cubes of their digits. That is, print numbers $abc$ that have the property $abc = a^3 + b^3 + c^3$\\ +\vspace*{0.2in} +\emphbar{These are called $Armstrong$ numbers.} +\end{frame} + +\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 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} + Write a program that accepts the starting value and prints out the Collatz sequence. +\end{frame} + +\begin{frame}[fragile]{Problem 1.3} + Write a program that prints the following pyramid on the screen. + \begin{lstlisting} +1 +2 2 +3 3 3 +4 4 4 4 + \end{lstlisting} +The number of lines must be obtained from the user.\\ +\pause +\emphbar{When can your code fail?} +\inctime{5} +\end{frame} + \section{Data structures} \subsection{Lists} \begin{frame}[fragile] \frametitle{Lists} \begin{block}{We already know that} \begin{lstlisting} -num = [1, 2, 3, 4, 5, 6, 7, 8] +num = [1, 2, 3, 4] \end{lstlisting} \centerline{is a list} \end{block} @@ -138,29 +238,76 @@ num = [1, 2, 3, 4, 5, 6, 7, 8] \begin{frame}[fragile] \frametitle{Lists: methods} \begin{lstlisting} -In []: num.reverse() +In []: num = [1, 2, 3, 4] + +In []: num.append([9, 10, 11]) + +In []: num +Out[]: [1, 2, 3, 4, [9, 10, 11]] + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Lists: methods} + \begin{lstlisting} +In []: num = [1, 2, 3, 4] + +In []: num.extend([5, 6, 7]) In []: num -Out[]: [8, 7, 6, 5, 4, 3, 2, 1] +Out[]: [1, 2, 3, 4, 5, 6, 7] -In []: num.extend([0, -1, -2]) +In []: num.reverse() In []: num -Out[]: [8, 7, 6, 5, 4, 3, 2, 1, 0, -1] +Out[]: [7, 6, 5, 4, 3, 2, 1] -In []: num.remove(0) +In []: num.remove(6) In []: num -Out[]: [8, 7, 6, 5, 4, 3, 2, 1, -1] \end{lstlisting} \end{frame} \begin{frame}[fragile] -\frametitle{List containership} + \frametitle{Lists: slicing} + \begin{itemize} + \item \typ{list[initial:final]} + \end{itemize} +\begin{lstlisting} +In []: a = [1, 2, 3, 4, 5] + +In []: a[1:3] +Out[]: [2, 3] + +In []: a[1:-1] +Out[]: [2, 3, 4] + +In []: a[:3] +Out[]: [1, 2, 3] +\end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Lists: slicing} + \begin{itemize} + \item \typ{list[initial:final:step]} + \end{itemize} \begin{lstlisting} -In []: a = 8 +In []: a[1:-1:2] +Out[]: [2, 4] + +In []: a[::2] +Out[]: [1, 3, 5] + +In []: a[-1::-1] +Out[]: [5, 4, 3, 2, 1] +\end{lstlisting} +\end{frame} -In []: a in num +\begin{frame}[fragile] +\frametitle{List containership} +\begin{lstlisting} +In []: 4 in num Out[]: True -In []: b = 10 +In []: b = 15 In []: b in num Out[]: False @@ -174,9 +321,14 @@ Out[]: True \frametitle{Tuples: Immutable lists} \begin{lstlisting} In []: t = (1, 2, 3, 4, 5, 6, 7, 8) + In []: t[0] + t[3] + t[-1] Out[]: 13 + +# Try the following! +In []: t[4] = 7 \end{lstlisting} +\pause \begin{block}{Note:} \begin{itemize} \item Tuples are immutable - cannot be changed @@ -200,7 +352,7 @@ They need not be of the same type! \subsection{Dictionaries} \begin{frame}[fragile] - \frametitle{Dictionaries: Recall} + \frametitle{Dictionaries: recall} \begin{lstlisting} In []: player = {'Mat': 134,'Inn': 233, 'Runs': 10823, 'Avg': 52.53} @@ -214,6 +366,28 @@ Out[]: 52.530000000000001 \end{block} \end{frame} +\begin{frame}[fragile] + \frametitle{Dictionaries: containership} + \begin{lstlisting} +In []: 'Inn' in player +Out[]: True + +In []: 'Econ' in player +Out[]: False + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Dictionaries: methods} + \begin{lstlisting} +In []: player.keys() +Out[]: ['Runs', 'Inn', 'Avg', 'Mat'] + +In []: player.values() +Out[]: [10823, 233, 52.530000000000001, 134] + \end{lstlisting} +\end{frame} + \begin{frame} {Problem Set 2.1: Problem 2.1.1} You are given date strings of the form ``29, Jul 2009'', or ``4 January 2008''. In other words a number, a string and another number, with a comma sometimes separating the items.\\Write a function that takes such a string and returns a tuple (yyyy, mm, dd) where all three elements are ints. \end{frame} @@ -228,32 +402,47 @@ You are given date strings of the form ``29, Jul 2009'', or ``4 January 2008''. \item >, >=, <, <=, in, \ldots \end{itemize} \begin{lstlisting} ->>> f10 = set([1,2,3,5,8]) ->>> p10 = set([2,3,5,7]) ->>> f10|p10 -set([1, 2, 3, 5, 7, 8]) ->>> f10&p10 -set([2, 3, 5]) ->>> f10-p10 -set([8, 1]) + +In []: f10 = set([1,2,3,5,8]) + +In []: p10 = set([2,3,5,7]) + +In []: f10 | p10 +Out[]: set([1, 2, 3, 5, 7, 8]) \end{lstlisting} \end{frame} \begin{frame}[fragile] - \frametitle{Set} + \frametitle{Set \ldots} \begin{lstlisting} ->>> p10-f10, f10^p10 -set([7]), set([1, 7, 8]) ->>> set([2,3]) < p10 -True ->>> set([2,3]) <= p10 -True ->>> 2 in p10 -True ->>> 4 in p10 -False ->>> len(f10) -5 +In []: f10 & p10 +Out[]: set([2, 3, 5]) + +In []: f10 - p10 +Out[]: set([1, 8]) + +In []: p10 - f10, f10 ^ p10 +Out[]: (set([7]), set([1, 7, 8])) + +In []: set([2,3]) < p10 +Out[]: True +\end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Set \ldots} + \begin{lstlisting} +In []: set([2,3]) <= p10 +Out[]: True + +In []: 2 in p10 +Out[]: True + +In []: 4 in p10 +Out[]: False + +In []: len(f10) +Out[]: 5 \end{lstlisting} \end{frame} @@ -261,7 +450,14 @@ False \frametitle{Problem set 2.2} \begin{description} \item[2.2.1] Given a dictionary of the names of students and their marks, identify how many duplicate marks are there? and what are these? - \item[2.2.2] Given a string of the form ``4-7, 9, 12, 15'' find the missing numbers in the given range. +\end{description} +\inctime{15} +\end{frame} + +\begin{frame} + \frametitle{Problem set 2.2} + \begin{description} + \item[2.2.2] Given a list of words, find all the anagrams in the list \end{description} \inctime{15} \end{frame} @@ -294,6 +490,19 @@ def signum( r ): \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 ): @@ -304,219 +513,13 @@ def what( n ): \end{lstlisting} \end{frame} -\subsection{Default arguments} -\begin{frame}[fragile] - \frametitle{Functions: default arguments} - \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{Built-in functions} -\begin{frame} - {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. -\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} - -\section{Modules} -\begin{frame}[fragile] - {Modules} -\begin{lstlisting} ->>> sqrt(2) -Traceback (most recent call last): - File "<stdin>", line 1, in <module> -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 latter 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} -\inctime{5} -\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{Objects} -\begin{frame}{Objects in general} - \begin{itemize} - \item What is an Object? (Types and classes) - \item identity - \item type - \item method - \end{itemize} -\end{frame} - -\begin{frame}{Almost everything is an Object!} - \begin{itemize} - \item \typ{list} - \item \typ{tuple} - \item \typ{string} - \item \typ{dictionary} - \item \typ{function} - \item Of course, user defined class objects! - \end{itemize} -\end {frame} - -\begin{frame}{Using Objects} - \begin{itemize} - \item Creating Objects: Initialization - \item Object Manipulation: Object methods and ``.'' operator - \end{itemize} -\end{frame} - -\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 Lists, Tuples, Dictionaries, Sets: creation and manipulation - \item More about functions - \item Coding style - \item Objects: creation and manipulation + \item Loops: \kwrd{while}, \kwrd{for} + \item Advanced Data structures + \item Functions \end{itemize} \end{frame} -\end{document} +\end{document}
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