Pippy

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The Pippy interface

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.

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

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

# Pascal's triangle
lines = 8

vector = [1]

for i in range(1,lines+1):
  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

size = 5
modulus = 2

lines = modulus**size

vector = [1]
for i in range(1,lines+1):
  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

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

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.

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

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 funcion, 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
loop = 1
breakpoint = 1000
pi = 0.0
while loop < breakpoint:
      pi = pi + (4.0/a) - (4.0/b);
      a = a + 4;
      b = b + 4;
      print pi;
      loop = loop + 1;
# 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

def square(x): 
    print x * x

square(3)
square(4)

If

Author: Chris Ball

number = input("Enter a number: ")

if number > 5:
    print "Greater than 5"
elif number < 5:
    print "Less than 5"
else:
    print "Number is 5!"

Recursion

Author: Mel Chua

# 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=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[0].upper() + word[1:].lower() 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 in range(len(names)):
    print x+1, names[x]

String

Hello1

Author: Chris Ball

print "Hello everyone!"

Hello2

Author: Chris Ball

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

# 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(0,50):
    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

import random
from random import randrange
R = randrange(1,100)


print "Guess a number between 1 and 100!!!"
N = 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=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 scrap.count(r) == 0]

      # 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 scrap.count(r) == 0]

      # update hero and robot positions
      hero = (hero[0] + commands[key][0],
              hero[1] + commands[key][1])
      def sign(x): return (x / abs(x)) if x else 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 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 = a + i
  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 = 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

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