1. An Introduction to Python Programming Dr. Mark Goadrich Centenary College of Louisiana http://mark.goadrich.com NWLAPCUG - May 15th 2008

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.

3. 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

4. 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 Many language choices: C++, Java, Prolog, Scheme, Perl, Fortran, Cobol, Ruby, etc…

5. Python Programming

6. How to Talk to your Computer ApplicationCPU User Programmer

7. Python Interpreter

8. Python and IDLE

9. Programming Components Five basic pieces to all programs –Data –User Interaction –Decisions –Repetition –Libraries

10. Data Storage and Memory Numbers 90 3.14159 2 + 3 / 4 * 5.6 Strings "The quick brown fox" "$5.48" Variables age = 31 cat = "Felix" length = 5 width = 10 area = length * width

11. 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)

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

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

14. 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"

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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!"

22. Running our Code Go to IDLE Open guess1.py Press F5 to run the program

23. 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...

24. 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

25. Guess A Number II print "Pick a number between 0 and 99, I will guess it." print "If I am high, type H, low, type L, and correct type C." low, high, correct = 0, 100, False while not correct: guess = (high + low) / 2 answer = raw_input("I guess " + str(guess) + ", HLC? ") if answer == "H": high = guess elif answer == "L": low = guess elif answer == "C": correct = True else: print "I don't understand, please enter H, L or C." print "I found it!"

26. Other Examples Chaos and Fractals Can’t Stop the Monkeys

27. Further References Python Home Page http://python.org How to Think Like a (Python) Programmer http://thinkpython.com Graphics Package for Python http://cs1graphics.org