An Overview of Programming in Python CSC 161: The Art of Programming Prof. Henry Kautz 9/9/2009 Slides stolen shamelessly from Dr. Mark Goadrich, Centenary College of Louisiana

Assignments Read the first chapter of the textbook Should be done! Assignment 1: Using IDLE Turn in assignment sheet today or Monday Only required to do steps 1 – 5 See revised steps 6 – 7 on the course web page Follow links from Calendar of Lectures, Workshops, & Labs Doing these steps is optional We will learn more about modules later in the course Workshops start: September 13/14/15 Required labs start: September 15/17 Why Computer Science 2

I’m Thinking of a Number… Can we guess the computer’s secret number between 0 and 100? Can the computer guess our secret number between 0 and 100? We need a common language to communicate.

Guess A Number Pseudocode Pick a random number for the computer Ask the user to guess the computer’s number While they guess wrong, Give feedback if number is too high or low Ask for another guess from the user Tell the user they are correct

Language of Programming English is a natural language Casual, slang, vague “I went to the bank.” (money or river?) Computers need formal languages Strict, specific, clear, unambiguous Our choice: Python In principle, all programming languages can do the same things 1 line of Python = 5 lines of Java = 20 lines of C = 100 lines of machine code Pseudocode Simple, (mostly) unambiguous English A way of getting from an English description to a real programming language

Elements of Programming Five basic pieces to all programs Data User Interaction Decisions Repetition Libraries

Data Storage and Memory Numbers / 4 * 5.6 Strings "The quick brown fox" "$5.48" Variables age = 31 cat = "Felix" length = 5 width = 10 area = length * width

User Interaction We need to ask the user questions age = input("How old are you? ") name = raw_input("What is your name? ") We want to tell the user the results print " In dog years, you are " + str(age * 7)

Decisions Relate variables with logic (True, False) temperature > 90 legs == 2 and not human Logic decides program path if temperature > 90: print " Must be summer again..." else: print " Looks like good weather." ?

Repetition Repeats commands while a condition is true count = 10 while count > 0: print count count = count - 1 print "Blastoff!" ?

Including Libraries Import functions from other places import random import math Use these functions to help our program if (random.random() < 0.5): print "Heads" else: print "Tails"

Guess A Number Translation Pick a random number for the computer Ask the user to guess the computer’s number While they guess wrong, Give feedback if number is too high or low Ask for another guess from the user Tell the user they are correct

Guess A Number Translation import random num = random.randrange(100) Ask the user to guess the computer’s number While they guess wrong, Give feedback if number is too high or low Ask for another guess from the user Tell the user they are correct

Guess A Number Translation import random num = random.randrange(100) guess = input("Try to guess my number 0-99: ”) While they guess wrong, Give feedback if number is too high or low Ask for another guess from the user Tell the user they are correct

Guess A Number Translation import random num = random.randrange(100) guess = input("Try to guess my number 0-99: ”) while num != guess: Give feedback if number is too high or low Ask for another guess from the user Tell the user they are correct

Guess A Number Translation import random num = random.randrange(100) guess = input("Try to guess my number 0-99: ”) while num != guess: if guess < num: print "Too Low!" else: print "Too High!" Ask for another guess from the user Tell the user they are correct

Guess A Number Translation import random num = random.randrange(100) guess = input("Try to guess my number 0-99: ”) while num != guess: if guess < num: print "Too Low!" else: print "Too High!" guess = input("Guess again: ”) Tell the user they are correct

Guess A Number Translation import random num = random.randrange(100) guess = input("Try to guess my number 0-99: ”) while num != guess: if guess < num: print "Too Low!" else: print "Too High!" guess = input("Guess again: ”) print "Correct!"

Part II - Computer Guesses How can the computer guess our number? The same way we guessed Start out with a range of numbers Each guess, split the answers in half Eventually, the range will be one number We’re now moving past programming to computer science...

Guess A Number II Print instructions to the user Initialize high and low boundaries and status of guess While guess is incorrect, Formulate a new guess halfway between boundaries Ask for user feedback on guess If guess too high, reset upper boundary If guess too low, reset lower boundary If correct, update status of guess Otherwise ask for valid input from the user When guess is correct, tell the user and exit

Elements of Python Literals Numbers Strings “Henry Kautz” Variables Holders for numbers, strings, lists, and other kinds of information Must begin with a letter, followed by letters, numbers, or underscore _ characters GradePointAverage grade_point_average gradePointAverage Why Computer Science 21

Expressions Made out of Literals Variables Operators (MidtermGrade + FinalGrade) / 2.0 FirstName + “ “ + LastName Functions (we’ll see one soon…) Assignment Statements = AverageGrade = (MidtermGrade + FinalGrade) / 2.0 FullName = FirstName + “ “ + LastName Why Computer Science 22 We use to indicate any thing that is of that type

How Assignments Work Evaluate the right-hand (expression) side Put the value in the left hand (variable) side Count = 1 Count = Count + 1 what is the value of Count? Assigning Input = input( ) guess = input(“What is your guess?”) Why Computer Science 23 the first function we have seen today

Conditional Execution if guess < num: print "Too Low!” else: print "Too High!” General form: if : else: Why Computer Science 24

Loops while num != guess: if guess < num: print "Too Low!” else: print "Too High!” General form: while : Why Computer Science 25

For Next Class Read Chapter 2 Pre-read Chapter 3 Finish Assignment 1 parts 1-5 if not already done Try new version of parts 6-7 if you like Remember: Lab sessions become mandatory starting next week Workshops start Sunday (or Mon/Tue) Why Computer Science 26