An Introduction to Python Programming

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An Introduction toPython Programming

• Dr. Mark Goadrich
• Centenary College of Louisiana
• http//mark.goadrich.com
• NWLAPCUG - May 15th 2008

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Im Thinking of a Number

• Can we guess the computers secret number between
  0 and 100?
• Can the computer guess our secret number between
  0 and 100?
• We need a common language to communicate.

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Guess A Number Pseudocode

• Pick a random number for the computer
• Ask the user to guess the computers 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

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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

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Python Programming
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How to Talk to your Computer
User
Application
CPU
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Python Interpreter
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Python and IDLE
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Programming Components

• Five basic pieces to all programs
• Data
• User Interaction
• Decisions
• Repetition
• Libraries

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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

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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)

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Decisions

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

?
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Repetition

• Repeats commands whilea condition is true
• count 10
• while count gt 0
• print count
• count count - 1
• print "Blastoff!"

?
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Including Libraries

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

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Guess A Number Translation

• Pick a random number for the computer
• Ask the user to guess the computers 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

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Guess A Number Translation

• import random
• num random.randrange(100)
• Ask the user to guess the computers 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

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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

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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

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Guess A Number Translation

• import random
• num random.randrange(100)
• guess input("Try to guess my number 0-99 ")
• while num ! guess
• if guess lt num
• print "Too Low!"
• else
• print "Too High!"
• Ask for another guess from the user
• Tell the user they are correct

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Guess A Number Translation

• import random
• num random.randrange(100)
• guess input("Try to guess my number 0-99 ")
• while num ! guess
• if guess lt num
• print "Too Low!"
• else
• print "Too High!"
• guess input("Guess again ")
• Tell the user they are correct

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Guess A Number Translation

• import random
• num random.randrange(100)
• guess input("Try to guess my number 0-99 ")
• while num ! guess
• if guess lt num
• print "Too Low!"
• else
• print "Too High!"
• guess input("Guess again ")
• print "Correct!"

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Running our Code

• Go to IDLE
• Open guess1.py
• Press F5 to run the program

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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
• Were now moving past programming to computer
  science . . .

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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

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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!"

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Other Examples

• Chaos and Fractals
• Cant Stop the Monkeys

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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