# Pippy

### From OLPC

Pippy
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# Description & Goals

### Summary

Teaches Python programming by providing access to Python code samples and a fully interactive Python interpreter.

The user can type and execute simple Python expressions. For example, it would be possible for a user to write Python statements to calculate expressions, play sounds, or make simple text animation.

The initial build ships with about twenty short Python examples covering various aspects of the language.

### Goals

- To introduce children to computer programming
- Give the possibility to the children to collaborate and share while doing computer programming.

### Collaboration

#### Wiki to contribute

Collaboration on this Wiki can help the keeper of Pippy by letting the community offer code snips and code lessons to draw from.

In a normal Python program one would not have comments about the language. That rule would be relaxed here to help the student or make a point.

#### Pippy

Pippy adventures can be shared with others in the neighborhood via the Sugar user interface. One way to share is to use the "Journal" after quitting a Pippy activity. Resume that activity with "Write" instead of Pippy. Then use the share Activity of Write to share the Plain text with others.

There may be other ways too.

# Examples

Please add examples here, or modify the existing ones!

## Math

### Apples

- Author: Madeleine Ball
- About: Adding and dividing
- Shows: Print Statements and Basic Math
- XOversion: Bundled in 656

print "Let's do math!" print "On Monday I picked 22 apples. On Tuesday I picked 12." print "Now I have: ", 22 + 12 print "My brother says he picked twice as many apples last week." print "This means he picked: ", (22 + 12) * 2 print "I have 3 friends to whom I would like to give apples." print "One third of my apples is about: ", (22 + 12) // 3 print "Or, more exactly: ", (22.0 + 12.0) / 3.0

### Pascal's triangle

- Author: Madeleine Ball
- About: Character graphic of Pascal's triangle
- Shows: loops, vectors
- XOversion: Bundled in 656

# Pascal's triangle lines = 8 vector = [1] for i in range(0,lines): vector.insert(0,0) vector.append(0) for i in range(0,lines): newvector = vector[:] for j in range(0,len(vector)-1): if newvector[j] == 0: print " ", else: print "%2d" % newvector[j], newvector[j] = vector[j-1] + vector[j+1] print vector = newvector[:]

### Sierpinski triangle

- Author: Madeleine Ball
- About: Character graphics of a Sierpinski triangle
- Shows: Modifying Pascal's triangle program, loops, vectors
- XOversion: Bundled in 656

size = 5 modulus = 2 lines = modulus**size vector = [1] for i in range(0,lines): vector.insert(0,0) vector.append(0) for i in range(0,lines): newvector = vector[:] for j in range(0,len(vector)-1): if newvector[j] == 0: print " ", else: remainder = newvector[j] % modulus if remainder == 0: print "O", else: print ".", newvector[j] = vector[j-1] + vector[j+1] print vector = newvector[:]

### Times1

- Author: Chris Ball
- About: The 4 times table
- Shows: Loops, the range statement
- XOversion: Bundled in 656

for i in range(1,13): print i, "x 4 =", (i*4)

### Times2

- Author: Chris Ball
- About: Print any times table
- Shows: Loops, range, and input
- XOversion: Bundled in 656

number = input("Which times table? ") for i in range(1,13): print i, "x", number, "=", i*number

### Fibonacci Series

- Author : Rafael Ortiz
- About: The Fibonacci Number Series
- Shows: Using tuple assignments. While loop.
- XOversion: Bundled in 656

a, b = 0, 1 while b < 1001: print b, a, b = b, a+b

### Stern-Brocot Tree

- Author: User:Walter modifying code from
*Pythonic Mathematics* - About: http://en.wikipedia.org/wiki/Stern-Brocot_tree
- Shows: Using class definitions, functions, yield
- XOversion:

# The Stern-Brocot tree contains every non-negative rational number # expressed in its lowest terms # Reference: Brian Hayes, Computing Science On the Teeth of Wheels, # American Scientist, July-August, Volume 88, No. 4, # define a class for rational numbers: # numerator / denominator class Rational: def __init__(self, num, den): self.num, self.den = num, den def __repr__(self): return str(self.num) + '/' + str(self.den) # define the mediant function # mediant (a/b, c/d) = (a+c)/(b+d) def mediant(a, b): return Rational(a.num + b.num, a.den + b.den) # expand a row by calculating mediants between each pair of elements # e.g., [0/1, 1/0] -> [0/1, 1/1, 1/0] def expand(row): x = [row[0]] for i in range(1, len(row)): x += [mediant(row[i-1], row[i])] + [row[i]] return x # initialize the first row with 0/1, 1/0 # each pass will yield an expanded row def rationals(): row = [Rational(0, 1), Rational(1, 0)] while True: yield row row = expand(row) # iterate through successive rows r = rationals() i = 1 while i<5: print r.next() i+=1

### Pythagoras

- Author : Rafael Ortiz
- About: Uses Pythagorean Theorem to compute longest edge of a triangle
- Shows: Import statement, sqrt (square root) function.

import math from math import sqrt print "This is the Pythagoras Theorem" a=float(raw_input("Type a =")) b=float(raw_input("Type b =")) c=sqrt((a*a)+(b*b)) print "c =",c

### Factorize

- Author: Reinier Heeres
- About: Factoring Numbers with trial divisions
- Shows: Appending to arrays, import, sys.stdout

import math import sys orignum = input("Enter a number to factorize ") factors = [] num = orignum i = 2 while i <= math.sqrt(num): if num % i == 0: factors.append(i) num /= i i = 2 elif i == 2: i += 1 else: i += 2 factors.append(num) if len(factors) == 1: print "%d is prime" % orignum else: sys.stdout.write("%d is %d" % (orignum, factors[0])) for fac in factors[1:]: sys.stdout.write(" * %d" % fac) print

### Zeros of a second degree polynomial

- Author: Pilar Saenz
- About: Zeros of a second grade polynomial, e.g., 3x^2+6x+3.
- Shows: Converting strings to float, import, sqrt (square root)

import math from math import sqrt print "These are the zeros of a second grade polynomial" a=float(raw_input("Type a =")) b=float(raw_input("Type b =")) c=float(raw_input("Type c =")) aux=b*b-4*a*c; if aux>0: x1=(-b+sqrt(aux))/(2*a) x2=(-b-sqrt(aux))/(2*a) print "x1= " , x1 ,", x2=" ,x2 elif aux==0: print "x= " , -b/(2*a) else: x1=(-b+sqrt(-aux)*1j)/(2*a) x2=(-b+sqrt(-aux)*1j)/(2*a) print "x1= " , x1 , ", x2" , x2

### Factorial of a number

- Author: Pilar Saenz
- About: Prints a factorial
- Shows: Defining and calling a function. Casting to int.

def factorial(a): fac=a for i in range(1,a): fac=fac*i print a,"!=",fac a=int(raw_input("Type a=")) factorial(a)

### Greatest common divisor

- Author: Pilar Saenz
- About: The greatest common divisor of two numbers
- Shows: The % (modulo) operator

n= input("Enter a number ") m= input("Enter another number ") r=n%m if r!=0: while (r!=0): n=m m=r r=n%m print "The greatest common divisor is ", m

### Windchill Calculator

- Author: Tyler Conlee
- About: Calculates the windchill given a temperature and a wind speed. For my high school senior project I learned about Linux and the OLPC Foundation. With the help of my mentor, Bill C. Smith, I learned simple Python programming. This program is one the items I turned in for the project. By placing in the /usr/share/activities/Pippy.activity/data/math directory it can appear under math examples in Pippy.
- Shows: The sys.exit function to stop a program, the round function, and Celsius to Fahrenheit conversion in a pratical math example.

###Windchill calculator for XO import sys Tscale = raw_input ("Enter F for Fahrenheit, or C for Celsius: ") if Tscale == 'F' or Tscale == 'f': print "Temperature is in Fahrenheit" elif Tscale == 'C' or Tscale == 'c': print "Temperature is in Celsius" else: print "Invalid temperature scale" ## sys.exit is used to stop the program. sys.exit(1) T = input("Enter a temperature: ") if Tscale == 'C' or Tscale == 'c': T = (9.0/5.0) * T + 32.0 if T > 50.0: print "Temperature must be <= 50F/10C" sys.exit(1) WSPD = input ("Enter the wind speed (mph):") if WSPD < 3.0: print "Wind speed must be >= 3 mph" sys.exit(1) WCL = 35.74 + 0.6215 * T - 35.75 * (WSPD**0.16) + 0.4275 * T * (WSPD**0.16) WCLC = (WCL - 32.0) * (5.0/9.0) # Round is used to round the answers. In this case to two decimal places. print "Windchill =", round (WCL, 2), "Fahrenheit" print "Windchill =", round (WCLC, 2),"Celsius"

### Compute pi!

Author: Travis Hall

Extended By: Tom Mitchell

Simple pi computation demo, does 1000 loops... to do more loops change the breakpoint varible to a higher number.Travis Hall

I have added a couple lines to explore various ways that floating point numbers might be printed. Tom Mitchell

a,b = 1.0,3.0 breakpoint = 1000 pi = 0.0 for loop in range(1, breakpoint): pi += (4.0/a) - (4.0/b) a += 4 b += 4 print pi # Now that the result has been computed we can explore printing the result. print "There are multiple ways to print numbers here is a quick sample." print "Just print it :", pi print "Using repr() :", repr(pi) print "Our approximation: %3.20f" % pi print "\nPi is a very famous number...." # Use python's math module it is faster and close enough for most computations. import math print "Python's Math library computes" print "a better value pi: %3.39f" % math.pi; # it uses...(math.atan(1.0) * 4.0) # when running computations based on "pi" it is good to begin with the best value you can get. # from the gnu 'C' comiler /usr/include/math.h" print "For reference a more exact 32 bit floating point value for pi is." print "Known value of pi: 3.14159265358979323846"

## Python

### Function

- Author: Chris Ball
- XOversion: Bundled in 656

def square(x): print x * x square(3) square(4)

### If

- Author: Chris Ball
- XOversion: Bundled in 656

number = input("Enter a number: ") if number > 5: print "Greater than 5" elif number < 5: print "Less than 5" else: print "Number is 5!"

### Count backwards with Recursion

- Author: Mel Chua with comments by Tom Mitchell
- XOversion: Bundled in 656

In a UCSD Pascal manual the classic glossary description for "recursion" was "see recursion". This is sort of inside joke is an example of recursion not an informative description.

An external link to Wikipedia is more informative.

Note how "countbackwards" is defined to use itself. Recursion can be a very clear and precise way to express some things in a program. It does have some disadvantages. Each time a recursive function calls itself the computer must push a return call onto the stack. If the recursion is very deep, stack exhaustion is possible.

# Note this assumes you understand functions and if-else. def countbackwards(number): print "I have the number", number if number > 0: print "Calling countbackwards again!" countbackwards(number-1) else: print "I am done counting" number = input("Enter a number: ") countbackwards(number):

### While

Author Pilar Saenz

n=input("enter a number") while n>0: print n, " ", n-=1 print "Surprise!\n"

### Title Case Capitalisation

Author: Alan Davies

# This is an example of a list comprehension oldtitle = "this TITLE iS NOW coRRecTly CAPItalised" oldwords = oldtitle.split() newwords = [word.capitalize() for word in oldwords] newtitle = " ".join(newwords) print "Before:", oldtitle print "After:", newtitle

### Names Drawn From a Hat

Author: Alan Davies

# Simple and possibly useful program for # drawing names in a random order from a hat import random names = [] name = raw_input("Enter the first name to go in the hat:") while name != "": names.append(name) name = raw_input("Enter another name, leave blank if you have finished:") random.shuffle(names) print "The random order from the hat is:" for x,name in enumerate(names): print x+1, name

## String

### Hello1

Author: Chris Ball

print "Hello everyone!"

### Hello2

- Author: Chris Ball
- XOversion: Bundled in 656

name = raw_input("Type your name here: ") print "Hello " + name + "!"

### Thanks

Author: Walter Bender

Comment: Please add names as appropriate

import random from random import choice table = { 'Hardware & Mechanicals': 'John Watlington, Mark Foster, Mary Lou Jepsen, Yves Behar, Bret Recor, Mitch Pergola, Martin Schnitzer, Kenneth Jewell, Kevin Young, Jacques Gagne, Nicholas Negroponte, Frank Lee, Victor Chau, Albert Hsu, HT Chen, Vance Ke, Ben Chuang, Johnson Huang, Sam Chang, Alex Chu, Roger Huang, and the rest of the Quanta team, the Marvell team, the AMD team, the ChiMei team..', 'Firmware': 'Ron Minnich, Richard Smith, Mitch Bradley, Tom Sylla, Lilian Walter, Bruce Wang..', 'Kernel & Drivers': 'Jaya Kumar, Jon Corbet, Reynaldo Verdejo, Pierre Ossman, Dave Woodhouse, Matthew Garrett, Chris Ball, Andy Tanenbaum, Linus Torvalds, Dave Jones, Andres Salomon, Marcelo Tosatti..', 'Graphics systems': 'Jordan Crouse, Daniel Stone, Zephaniah Hull, Bernardo Innocenti, Behdad Esfahbod, Jim Gettys, Adam Jackson, Behdad Esfahbod..', 'Programming': 'Guido Van Rossum, Johan Dahlin, Brian Silverman, Alan Kay, Kim Rose, Bert Freudenberg, Yoshiki Ohshima, Takashi Yamamiya, Scott Wallace, Ted Kaehler, Stephane Ducasse, Hilaire Fernandes..', 'Sugar': 'Marco Pesenti Gritti, Dan Williams, Chris Blizzard, John Palmieri, Lisa Strausfeld, Christian Marc Schmidt, Takaaki Okada, Eben Eliason, Walter Bender, Tomeu Vizoso, Simon Schampijer, Reinier Heeres, Ben Saller, Miguel Alvarez..', 'Activities': 'Erik Blankinship, Bakhtiar Mikhak, Manusheel Gupta, J.M. Maurer (uwog) and the Abiword team, the Mozilla team, Jean Piche, Barry Vercoe, Richard Boulanger, Greg Thompson, Arjun Sarwal, Cody Lodrige, Shannon Sullivan, Idit Harel, and the MaMaMedia team, John Huang, Bruno Coudoin, Eduardo Silva, H&?kon Wium Lie, Don Hopkins, Muriel de Souza Godoi, Benjamin M. Schwartz..', 'Network': 'Michael Bletsas, James Cameron, Javier Cardona, Ronak Chokshi, Polychronis Ypodimatopoulos, Simon McVittie, Dafydd Harries, Sjoerd Simons, Morgan Collett, Guillaume Desmottes, Robert McQueen..', 'Security': 'Ivan Krstic, Michael Stone, C. Scott Ananian, Noah Kantrowitz, Herbert Poetzl, Marcus Leech..', 'Content': 'SJ Klein, Mako Hill, Xavier Alvarez, Alfonso de la Guarda, Sayamindu Dasgupta, Mallory Chua, Lauren Klein, Zdenek Broz, Felicity Tepper, Andy Sisson, Christine Madsen, Matthew Steven Carlos, Justin Thorp, Ian Bicking, Christopher Fabian, Wayne Mackintosh, the OurStories team, Will Wright, Chuck Normann..', 'Testing': 'Kim Quirk, Alex Latham, Giannis Galanis, Ricardo Carrano, Zach Cerza, John Fuhrer..', 'Country Support': 'Carla Gomez Monroy, David Cavallo, Matt Keller, Khaled Hassounah, Antonio Battro, Audrey Choi, Habib Kahn, Arnan (Roger) Sipitakiat', 'Administrative Support': 'Nia Lewis, Felice Gardner, Lindsay Petrillose, Jill Clarke, Julia Reynolds, Tracy Price, David Robertson, Danny Clark', 'Finance & Legal': 'Eben Moglen, Bruce Parker, William Kolb, John Sare, Sandra Lee, Richard Bernstein, Jaclyn Tsai, Jaime Cheng, Robert Fadel, Charles Kane (Grasshopper), Kathy Paur, Andriani Ferti', 'PR and Media': 'Larry Weber, Jackie Lustig, Jodi Petrie, George Snell, Kyle Austin, Hilary Meserole, Erick A. Betancourt, Michael Borosky, Sylvain Lefebvre, Martin Le Sauteur', 'Directors & Advisors': 'Howard Anderson, Rebecca Allen, Ayo Kusamotu, Jose Maria Aznar, V. Michael Bove, Jr., Rodrigo Mesquita, Seymour Papert, Ted Selker, Ethan Beard (Google); John Roese (Nortel); Dandy Hsu (Quanta); Marcelo Claure (Brightstar); Gary Dillabough (eBay); Gustavo Arenas (AMD); Mike Evans (Red Hat); Ed Horowitz (SES Astra); Jeremy Philips (NewsCorp); Scott Soong (Chi Lin); Sehat Sutardja (Marvell); Joe Jacobson (MIT Media Lab); Steve Kaufman (Riverside); and Tom Meredith (MFI)', 'Pippy': 'Chris Ball' } print "OLPC would like to take this opportunity to acknowledge the community of people and projects that have made the XO laptop possible." subsystem = random.choice(table.keys()); print subsystem, '\t',table[subsystem]

## Graphics

### Jump

- Author: C. Scott Ananian
- XOversion: Bundled in 656

# both of these functions should be in the 'basic' package or some such def clear_scr(): print '\x1B[H\x1B[J' # clear screen, the hard way. def wait(): import time time.sleep(0.1) # jumping man! # was having to escape the backslash which was rather unfortunate, # now using python's r" strings which were meant for regex's # i didn't have to do that in C64 BASIC for i in xrange(50): clear_scr() print r"\o/" print r"_|_" print r" " wait() clear_scr() print r"_o_" print r" | " print r"/ \ " wait() clear_scr() print r" o " print r"/|\ " print r"| |" wait() clear_scr() print r"_o_" print r" | " print r"/ \ " wait()

### Mandelbrot Set

Author: Alan Davies

# Text-based Mandelbrot set generator # Play with the values of 'centre' and 'realsize' # to explore the set. centre, realsize, maxiter = -.7+0j, 2.8, 50 width, height, aspect = 60, 30, 1.9 charmap = "abcdefghijklmnopqrstuvwxyz" for y in range(height): output = "" for x in range(width): real = (float(x)/width-.5)*realsize imag = (float(y)/height-.5)*aspect*realsize*height/width z = c = complex(real, imag) + centre iterations = 0 while abs(z) < 2 and iterations < maxiter: z = z**2 + c iterations += 1 if iterations == maxiter: output += " " else: output += charmap[iterations%len(charmap)] print output

## Games

### Guess a number

- Author: Pilar Saenz
- XOversion: Bundled in 656

import random from random import randrange R = randrange(1,100) print "Guess a number between 1 and 100!!!" N = int(raw_input("Enter a number: ")) i=1 while N!=R: if N>R : print "Too big... try again" else : print "Too small.. try again" N = input("Enter a number: ") i+=1 print "You got it in ", i, "tries"

### Robots

Author: Alan Davies

This is a playable implementation of Robots (also known as Daleks). I tried to keep the code clear and well commented, even at the expense of space. I also made sure that the lines don't wrap in Pippy, as that looks quite ugly.

I'm not sure if this is considered too large for the samples to be included with Pippy- a simpler implementation could be trimmed down considerably. I figured it might be nice to have at least one complete implementation for kids and adults to play with.

from random import randint import curses stdscr = curses.initscr() curses.noecho() xmax, ymax, alive = 60, 10, True commands = {"q":(-1,-1), "w":(0,-1), "e":(1,-1), "a":(-1,0), "s":(0,0), "d":(1,0), "z":(-1,1), "x":(0,1), "c":(1,1), " ":(0,0), "t":(0,0)} def message(text, yoffset=0, wait=True): stdscr.addstr(ymax/2+yoffset, xmax/2-len(text)/2, text) stdscr.refresh() if wait: stdscr.getch() message("Welcome to Robots!", -3, False) message(" QWE Screwdriver: S ", -1, False) message("Movement: A D Teleport: T ", 0, False) message(" ZXC Do nothing: Spacebar", 1, False) message("Press any key...", 3) while True: level = 1 alive = True while alive: # Initialise powers, hero position, and enemy lists teleport = screwdriver = True hero = (xmax/2, ymax/2) scrap = [(randint(0, xmax), randint(0, ymax)) for dummy in range(level/3+3)] robots = [(randint(0, xmax), randint(0, ymax)) for dummy in range(level*4-3)] scrap = [s for s in scrap if s != hero] robots = [r for r in robots if r != hero] while True: # move crashed robots to scrap list scrap += [r for r in robots if robots.count(r) >= 2] robots = [r for r in robots if r not in scrap] # draw the screen stdscr.clear() stdscr.addstr(hero[1], hero[0], "@") for robot in robots: stdscr.addstr(robot[1], robot[0], "$") for scr in scrap: stdscr.addstr(scr[1], scr[0], "#") if screwdriver: stdscr.addstr(ymax-1, xmax+1, "S") stdscr.addstr(ymax, xmax+1,"T" if teleport else "") stdscr.refresh() # test for win or loss if len(robots) == 0: break elif hero in robots or hero in scrap: stdscr.addstr(hero[1], hero[0], "X") message("You lost! Press any key...") alive = False break # get a valid keypress key = "" while key not in commands: key = chr(stdscr.getch()).lower() # teleport - move to a random location if teleport and key == "t": teleport = False hero = (randint(0, xmax), randint(0, ymax )) # sonic screwdriver - scraps nearby robots if screwdriver and key == "s": screwdriver = False scrap += [robot for robot in robots if abs(robot[0] - hero[0]) <= 1 and abs(robot[1] - hero[1]) <= 1] robots = [r for r in robots if r not in scrap] # update hero and robot positions hero = (hero[0] + commands[key][0], hero[1] + commands[key][1]) def sign(x): return cmp(x, 0) def follow(fr, to): return (fr[0] + sign(to[0]-fr[0]), fr[1] + sign(to[1]-fr[1])) robots = [follow(robot, hero) for robot in robots] # move to next level if alive: level += 1 message(" Level %d! Press any key... " % level)

## Beginning Programming

### Operations on Numbers

- Author: Tom Mitchell
- About: addition, subtraction, multiply, divide. power(exponents) and modulo arithmetic
- Shows: basic arithmetic with integer and floating point numbers.

# Understanding how a computer works with numbers is interesting. # Python (Pippy) supports the basic set of operators on integers, floating point, decimal numbers and more. # This exercise will look at integers and floating point numbers. # Look at these samples and when you think you have the answer click run. # Change the numbers and experiment... # Add print 6 + 1 # Subtract print 6 - 1 # Multiply print 6 * 2 # Division - hint, dividing integers by integers result in integers. print 3/6 print 3.0/6.0 print 1/3 # integer print 1.0/3.0 # floating point # Modulo (remainder).. print 1%3 print 3%6 print 1.1234%3.0 print 3%2 print 3.0%2 # Power or exponents print 2**2 print 3**6 print 3.3**22

### Parentheses and Operators

- Author: Tom Mitchell
- About: Parentheses with addition, subtraction, multiply, divide, power(exponents) and modulo arithmetic
- Shows: basic arithmetic precidence rules and the use of parentheses.

# Understanding the order with which a computer works with numbers is interesting. # Python (Pippy) supports the basic set of operators on integers, floating point, decimal numbers and more. # This exercise will look at Pythons rules for basic integers and floating point operations and the use of parentheses. # Note the assignment to a variable and then the use of print to display a result. # Look at these samples and when you think you have the answer click run. # Change the numbers and experiment. # Regroup numbers and operators with parentheses to clarify what you want Python to do. # Add and Multiply some numbers but what is done first: # is is multiply or add; # is the order left to right or is it right to left. answer = 6 + 2 * 3 print answer answer = (6 + 2) * 3 print answer answer = 6 + (2 * 3) print answer # now exponents.. answer = 3.3**(20+2)+10 print answer answer = 3.3**(20)+ -(2+10) print answer # To convert from degrees Fahrenheit to Centigrade we can use an equation. F = 212 # but which equation is correct: C1, C2, C3 or C4? C1 = (F - 32.0)/ 9.0 * 5 C2 = F - 32.0/ 9.0 *5 C3 = F - (32.0/ 9.0) *5 C4 = F - 32.0/ (9.0 *5) print C1 print C2 print C3 # Why are C2 and C3 the same. print C4 # hint Water boils at 212 F and 100 C; Water freezes at 0 C and 32 F. F = 32.0 C = (F - 32.0)/ 9.0 * 5 print C print "%f F degrees converts to %3.10f C" %( F ,C) # Question what is interesting about -40 degrees? """ In Algebra one might write: 3 + 3 + 5 + 55 x = ---------------------- 22 """ # The next line is incorrect because the division only involves 55 x = 3.0 + 3 + 5 + 55 / 22 # This line is correct xx = (3.0 + 3 + 5 + 55) / 22 print "This is incorrect %i" % x print "This is correct %i" % xx # Question what is interesting about -40 degrees? # Hint -- use parentheses to clarify what you want Python to do. # Doing so you can make it clear to others what you intend.

### Take Pippy for a Loop

- Author: Tom Mitchell
- About: Looping
- Shows: While and for loops introduces a generator.

#! /usr/bin/python """ The Gauss Schoolroom Anecdote: A teacher once was inclined to assign long tedious problems to students. One problem was to add all the numbers from 1 to 100 or more. A student "Gauss" turned over his slate moments after starting the problem to signal that he was finished. His slate had a single number on the back ... 5050. How did he solve this so quickly? Who is "Gauss"? """ # lets explore loops to check the answer. # first a "while loop". i = 1 a = 0 while i <= 100: a += i i += 1 print a # now a "for loop" using the generator range() a = 0 for i in range(100+1): # the +1 is because range() returns a list N long a += i # that begins with 0. More on generators like range(N) later. print a # Will this get the correct answer? If so why? last = 100.0 print last * (1 + last ) / 2 """ Additional reading http://www.math.uwaterloo.ca/navigation/ideas/grains/gauss.shtml """

Loops do not need to be restricted to numbers. Try this little loop.

for tree in "oak", "maple", "plum": print tree

### Printing various Number Types in Pippy

- Author: Tom Mitchell
- About: Formatting when printing numbers
- Shows: type(), if, elif, else and the use of % in formatting of numbers.

#! /usr/bin/python import decimal a = 1.5 b = 55 c = -55.12345 d = True e = 5555555555555555555555555555L f = 4444444444444444444444444444.12345678 g = 55.77e22 h = 'string' i = decimal.Decimal("3333333333333333333333333333.12345678") j = decimal.Decimal("2222222222222222222222222222.12345678") k = i * j k = k * k * k # should now be very big l = 0567 # hint this is octal i.e. base 8 m = 0x456ABCD # base 16 i.e hex for thing in [ a, b, c, d, e, f, g, h, i, j, k, l, m ]: print "========================" print "printing it ",thing # print type(thing) if type(thing) is float: print "found a float", thing print "float can be formatted: %f " % thing print "float can be formatted: %4.9f " % thing print "float can be formatted: %1.5f " % thing print "float can be formatted: %1.3e " % thing print "float can be formatted: %1.1E " % thing elif type(thing) is int: print "found a int ", thing print "int can be formatted: %i # right justified" % thing print "int can be formatted: %+25i # right justified with sign" % thing print "int can be formatted: %-25i # left justified" % thing print "int can be formatted: %+25i # right justified with sign" % thing print "int can be formatted as hex: %-+20x # Hex left justified with sign" % thing print "int can be formatted as hex: 0x%-20x # Hex left justified make it look like Hex " % thing print "int can be formatted as hex: 0x%+20X # Hex signed right justified bad try at looking like Hex" % thing print "int can be formatted as hex: %#-20X # Hex left justified make it look like Hex best way" % thing print "int can be formatted as hex: %#20X # Hex right justified make it look like Hex best way" % thing print "int can be formatted as hex: %#+20X # Hex signed right justified make it look like Hex best way" % thing print "int can be formatted as octal: %o # Octal" % thing print "int can be formatted as octal: 0%o # Octal make it look octal " % thing print "int can be formatted as octal: 0%-15o # Octal left justified, make it look octal incorrectly " % thing print "int can be formatted as octal: 0%15o # Octal make it look octal incorrectly and why" % thing print "int can be formatted as octal: %#o # Octal make it look octal correctly" % thing print "int can be formatted as octal: %#15o # Octal make it look octal correctly" % thing print "int can be formatted as octal: %#-15o # Octal left justified correctly" % thing elif type(thing) is long: print "found a long ", thing print "long can be formatted: %i " % thing # right justified is the default print "long can be formatted: %+i signed " % thing # right justified with sign print "long can be formatted as hex: %x " % thing # Hex print "long can be formatted as hex: 0x%x " % thing # Hex lower case print "long can be formatted as octal: %o " % thing # Octal print "long can be formatted as octal: %#o " % thing # Octal make look like octal elif type(thing) is str: print "found a str ", thing elif type(thing) is decimal.Decimal: print "found a decimal.Decimal ", thing print "decimal.Decimal can be formatted: %1.5f " % thing print "decimal.Decimal can be formatted: %1.3e " % thing print "decimal.Decimal can be formatted: %1.3E " % thing print "decimal.Decimal can be formatted: %55.55e " % thing else: print "this type is not in my list" # this will trip on the boolian "True" for d. """ Make changes to the above and see what changes. Shorten the list to focus on one type or another. Formating of numbers builds on the C library so the % formats are best described by looking at the printf man page. Use the web and search for: PRINTF(3) Linux Programmer's Manual PRINTF(3) .... Format of the format string The format string is a character string, beginning and ending in its initial shift state, if any. The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each con- version specification is introduced by the character '%', and ends with a conversion specifier. In between there may be (in this order) zero or more flags, an optional minimum field width, an optional precision and an optional length modifier. .... and lots more ... """

### Comparing objects in Pippy

- Author: Tom Mitchell
- About: Comparisons and tests >, <, <=, >=, ==, not
- Shows: Shows some very introductory ways to build truth tables.

This is a bit long but the goal here is to show how to build some skills with tests and truth tables.

#! /usr/bin/python # Comparison tests are the key to program flow and decisions. # All objects can be compared.... """ from the Python Library Reference. < strictly less than <= less than or equal > strictly greater than >= greater than or equal == equal != not equal (prefered over <> ) <> not equal (not prefered) is object identity is not negated object identity Boolean Operations x or y if x is false, then y, else x (1) x and y if x is false, then x, else y (1) not x if x is false, then True, else False (2) 1) These only evaluate their second argument if needed for their outcome. (2) "not" has a lower priority than non-Boolean operators, so not a == b is interpreted as not (a == b), and a == not b is a syntax error. """ a = 1 b = 2 # could also do "a, b = 1, 2" # - - - - - - - - - - - - - - - - - - - - print "\n===============================" print "Control program flow with an if" if a < b : print "Less Than" # - - - - - - - - - - - - - - - - - - - - print "\n===============================" print "Looping while a test stays true" a, b = 1, 4 while a < b: print "a is still less than b" b -= 1 # same as "b = b -1" # - - - - - - - - - - - - - - - - - - - - print "\nBreak out of a loop when a test becomes true" a, b = 1, 4 while a < b: print "a is still less than b" b += 1 c = b # One common error in JavaScript and C is confusing # assignment '=' and a test for equality '=='. # Uncoment this block and see what happens. # if c = 10: # print "Exit on assignment not equality" # break if b == 10: print "Exit the loop \'b\' is now ten." break # - - - - - - - - - - - - - - - - - - - - print "\nBreak out of a loop when a test becomes true" a, b = 1, 4.0000000001 while a < b: print "a is still less than b" b += 1 c = b # testing floating point numbers for exact equality is problematic. if b == 10: print "Exit the loop \'b\' is now ten." break if b >= 10: print "Exit the loop \'b\' is now ten or more." break # - - - - - - - - - - - - - - - - - - - - T, F = True, False # what is the truth table for 'or', 'and', 'not' ? print "\n===============================" print "Exploring Boolean\'s \'or\'." if F or F: print "F or F tests true" if T or F: print "T or F tests true" if F or T: print "F or T tests true" if T or T: print "T or T tests true" # - - - - - - - - - - - - - - - - - - - - print "\n===============================" print "Exploring Boolean\'s \'and\'." if F and F: print "F and F tests true" if T and T: print "T and T tests true" if T and F: print "T and F tests true" if F and T: print "F and T tests true" # - - - - - - - - - - - - - - - - - - - - print "\n===============================" print "Exploring Boolean\'s \'not\'." if not(F or F): print "not(F or F) tests true" if not(T or T): print "not(T or T) tests true" if not(T or F): print "not(T or F) tests true" if not(F or T): print "not(F or T) tests true" if not(F and F): print "not(F and F) tests true" if not(T and T): print "not(T and T) tests true" if not(T and F): print "not(T and F) tests true" if not(F and T): print "not(F and T) tests true" if not F or F: print "not F or F tests true" if not T or T: print "not T or T tests true" if not T or F: print "T or F tests true" if not F or T: print "not F or T tests true" if not F and F: print "not F and F tests true" if not T and T: print "not T and T tests true" if not T and F: print "not T and F tests true" if not F and T: print "not F and T tests true" # - - - - - - - - - - - - - - - - - - - - print "\n===============================" print "Exploring comparisons of strings'." lc="lower case string" UC="Upper Case string" if lc == UC: print "String test:\n \"%s\" is the same as \"%s\" ." % (lc, UC) else: print "String test:\n \"%s\" is NOT the same as \"%s\" " % (lc, UC)

### Lists, Tuples, Sets and more

- Author: Tom Mitchell
- About: Lists, tuples, sets and some string tinkering
- Shows: Introduction to ways to define and convert from one to the other.

#! /usr/bin/python """ Lists, Tuples, Sets and Dictionaries: Data structures are fundamental to programing. In python most data structures are built with tuples, sets, lists and dictionaries. Data structures are how data is organized and passed to and from functions. """ # lists are bounded by "[]" a sequence of objects that can be modified. print "\nExploring Lists:" Bob, Carol, Ted = "Bob Johnson", "Carol Johnson", "Ted Turner" somenames = [ Bob, Carol, Ted ] sometrees = ["teak", "oak", "pine"] sometrees = sometrees + ["maple", "apple"] print sometrees sometrees[2] = "willow" # legal for lists print sometrees # tuples are bounded by "()" , cannot modify a tuple's contents. print "\nExploring tuples:" nums = (1, 2, 3, 5.01) trees = ("teak", "oak", "pine") bushes = "blueberry", "Sage" # when expected a tuple is assumed. tuptup = (nums, trees, bushes) # This is illegal for a tuple. Uncomment it and try. #nums[2] = 55 print nums, trees, bushes # print EXPECTS a tuple print (nums, trees, bushes, "Tuple") # print EXPECTS a tuple print tuptup # sets are introduced by the key word "set", and no duplicates no special order print "\nExploring sets:" aa = set("Happy is Pippy") print aa # how many p's and y's will be printed? # dictionaries are bounded with {} and use : with , to associate pairs. print "\nExploring dictionaries:" telescope = { 'mirror' : 'reflection', # three ways to indicate strings ' "lens" : "refraction", # " """Hubble""" : """reflector""", # and the triple """ "Cassegrain" : "reflector", "Great Lick" : "refractor" } print telescope["Hubble"] # strings are are bounded with ' or " or """. It makes some sense # to include them here. print "\nExploring strings:" # The following string is interesting in English, but why? s1 = "The quick brown FOX jumped over the lazy dogs" print s1 # some things are easy to do with strings. print s1[4:9] print s1.upper() print s1.swapcase() print s1.title() # sorting and moving the characters about is not one of them. # sorting is easy to do in a list. sL = s1.lower() l1= list(sL) l1.sort() print l1 print "" s2= "".join(l1) # "" is the (empty) string seperating the objects providing the method sX= "X".join(l1) # "X" is the string seperating the objects providing the method print s2 print sX # sets can only have one of each. t1=set(l1) print t1 L2= list(t1) L2.sort() S1="".join(L2) print "It might be clear what is fun about the phrase now.\n" + S1

### Functions lots of functions

- Author: Tom Mitchell
- About: functions
- Shows: Shows lots function permutations

#! /usr/bin/python """ # Functions are a critical part of programming. # This File explores some of the ways to pass # information into a function and back out. # # The design of a program and function often centers on how data # is passed into and out of the function. This is commonly refered to # as the "interface". Clearly documenting the interface is important # and can be as simple as well chosen function and variable names, or coments. # An interface has three key parts: input, output and error. # # A function is introduced by the opertor "def" # # def FunctionName(tupple of inpupt ): # indented code # more indented code # Watch out for tabs, # a tab is one character but may look like up to 8 spaces. # more indented code.... Smart editors may confuse the handling of tabs. # Python does expand tabs and assumes up to 8 char. Good style is to # use one or the other. i.e. Try to not mix spaces and tabs in python source. # See: http://docs.python.org/ref/indentation.html # # A function can take advantage of other functions. # An ideal function returns a result and does not modify data # outside of it's own scope. """ # - - - - - - - - - - - - - - - - - - - - - - - - - - - - # The cannocal Hello World can be writen in Python thusly print "\n================\nExample function: \"Hello\"" def Hello(): print "Hello World\n" # now call it Hello() # - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Simple data can be passed to a function. print "\n================\nExample function: \"Twice\"" def Twice(x): """Twice uses + to operate on a single input object. This is a good place to introduce documentation... The first line should be short and precise. The second doc line should be blank. In this style of documentation the information stays with the object even if it is complied to byte code. """ print x + x Twice(5) Twice("Cat") print (Twice.__doc__) # # - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Multiple data objects can be passed to a function by position. print "\n================\nExample function: \"Volume\"" def Volume(L, W, H): """Length times Width times Height is Volume of a rectangular box""" V = L * W * H return(V) L1, W1, H1 = 5, 6, 2 V1= Volume(L1, W1, H1) print("The volume of a box %i x %i x %i is %i" % (L1, W1, H1, V1)) # - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Multiple data objects can be passed to a function by name. print "\n================\nExample function: \"PetFood\"" def PetFood(cat=0, dog=0, bird=0): # a house cat eats 25 gr of cat food per day. catfood = 25 * cat # a dog eats 100 gr of dog food per day. dogfood = 100 * dog # a bird eats 15 gr of bird food per day. birdfood = 15 * bird print "\n\tHow much Cat, Dog and Bird food?" print "\tWith %i cats we need %i gr of catfood." % (cat, catfood) print "\tWith %i dogs we need %i gr of dogfood." % (dog, dogfood) print "\tWith %i birds we need %i gr of birdfood." % (bird, birdfood) print "\tAll together the full bag should weigh about %i gr." % (catfood+dogfood+birdfood) return (cat, catfood, dog, dogfood, bird, birdfood) PetFood(cat=5, bird=10) # note that 'dog' has a default value of 0. print PetFood(dog=12, cat=5, bird=10)

### execv() of another python file in Pippy

- Author: Tom Mitchell
- About: execv()
- Shows: Shows how to run a file that might be edited in a terminal Activity"

This is a bit advanced but someone asked in the discussions. One value is that is much the way Python programmers work.

First in a terminal Activity use vim to generate a short python program like this:

#!/usr/bin/python print "this file is /tmp/t1.py" print "Fun with Python and Pippy"

Now make it executable:

chmod +x /tmp/t1.py

Next start Pippy and enter this code:

import os f2="/tmp/t1.py" print "================\nGetting ready to leave " os.execv(f2, ("/tmp/t1.py", "Additional args here")) print "N.B. This line is never reached"

### Slice notation

- Author: Stuart Morrow
- Shows: The using the slice notation on subscriptable data in Python

Some of the more advanced examples on this page just dive in to list/string slicing without explaining.

print "A list is an order collection of things" things = ['bike', 'tree', 'the Sun'] print things print print """You can access individual thing using the slice and a number The first thing is numbered 0, not 1""" thing = things[0] print "The third thing is numbered 2" thirdThing = things[2] print thing; print thirdThing print print """You can access more than one thing at a time if you use two numbers and a colon (:) things[start : howMany] finds things[start], then shows howMany things""" twoThings = things[0:2] threeThings = things[0:3] print "twothings =", twoThings, "and threeThings =", threeThings print print """If you specify a third number called the step or increment, you can take howMany things at regular intervals, instead of strictly one next to the other""" things = things * 3 print "things[0:7:1] is:" print things[0:7:1] print "things[0:7:2] is:" print things[0:7:2] print print """A list of numbers will be clearer now that we are learning increments""" numbers = range(5) # This is the same as numbers=[0,1,2,3,4] print numbers[1] # 'range' is English for ... print numbers [1:5:1] print numbers [1:5:2] print numbers [5:1:-1] print print """Words and sentences are subscriptable according to the same rules as lists and tuples""" print "'I am a sentence'[0] is", "I am a sentence"[0] print "'I am a sentence'[7:15] is", 'I am a sentence'[7:15] print """Note that the spaces between words are significant. "We are some words" is the same as ['W','e',' ','a','r','e',' ',...] ^ ^""" print list('We are some words')[0:10] print print """Conveniently, -1 is the last element of a subscriptable and -2 is the second-last, and so on""" print 'I am a sentence'[-1] print 'I am a sentence'[-8:-1] print print """The final section of this list-slicing is about omitting the numbers If you use [:x] it is the same as [0:x]""" print things[:3]; print things[0:3] print """If you do not specify the second index it is the same as saying "until the end of the list" """ print numbers[3:]; print numbers[3: len(numbers) ] print """Therefore, numbers[::] == numbers[:] == numbers""" print numbers; print numbers[:] print "And," string = things[0] print string, string[::-1]; print print "Finally," print "See that string[:n] + string[n:] == string" print string; print string[:1] + string[1:] print """Further Note that things[::-1] is not the same as things.reverse()""" print things.reverse() # Nothing! print things # ah, There it is print """You might liken this to the difference between list.sort() and sorted(list) Slices can be used anywhere a list can, so you can use them in tuple assignment for example""" (a, b) = "abcdefghijklmnop"[:2] print (a, b)

### More Examples

C. Scott Ananian created a small library of programming examples, based on the BASIC examples in the Commodore 64 manual. It can be found at http://dev.laptop.org/git?p=users/cscott/pippy-examples;a=tree

# See also

- Canvas tutorial is a similar environment to learn JavaScript and <canvas> programming, it runs in Browse.

**Activity Summary**

Icon: | Image:Pippy-icon.png |

Genre: | Programming |

Activity group: | Activities/G1G1 |

Short description: | warning.png"Activity for learning Python programming:Pippy provides access to Python code samples and a fully interactive Python interpreter.
The user can type and execute simple Python expressions. For example, it would be possible for a user to write Python statements to calculate expressions, play sounds, or make simple text animation. The initial build ships with about twenty short Python examples covering various aspects of the language." cannot be used as a page name in this wiki. |

Description: | |

Maintainers: | User:cjb |

Repository URL: | http://dev.laptop.org/git?p=projects/pippy-activity |

Available languages: | |

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Pootle URL: | |

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URL from which to download the latest .xo bundle | http://dev.laptop.org/~cscott/bundles/Pippy-30.xo |

Last tested version number: | 30 |

The releases with which this version of the activity has been tested. | |

Development status: | |

Ready for testing (development has progressed to the point where testers should try it out): | |

smoke tested : | |

test plan available : | |

test plan executed : | |

developer response to testing : |

URL from which to download the last .xo bundle that works with old releases | http://dev.laptop.org/~erikos/bundles/0.82/Pippy-25.xo |

Activity version number: | warning.png"" is not a number. |

The releases with which this version of the activity has been tested. | |

Development status: |

Activity bundle | http://dev.laptop.org/~cscott/bundles/Pippy-30.xo +, and http://dev.laptop.org/~erikos/bundles/0.82/Pippy-25.xo + |

Activity genre | Programming + |

Activity group | Activities/G1G1 + |

Activity version | 30 +, and warning.png"" is not a number. |

Contact person | Cjb + |

Localization URL | http://dev.laptop.org/git?p=projects/pippy-activity;a=blob_plain;f=po/Pippy.pot;hb=HEAD + |

Short description | warning.png"Activity for learning Python programming:Pippy provides access to Python code samples and a fully interactive Python interpreter.
The user can type and execute simple Python expressions. For example, it would be possible for a user to write Python statements to calculate expressions, play sounds, or make simple text animation. The initial build ships with about twenty short Python examples covering various aspects of the language." cannot be used as a page name in this wiki. |

Source code | http://dev.laptop.org/git?p=projects/pippy-activity + |

Sugar icon | + |