1 Computer Graphics and Games MONT 105S, Spring 2009 Lecture 2 Simple Python Programs Working with numbers and strings

2 Review Write a program that asks for a user's favorite food, and then says that it likes that food too. # Program: food.py # Purpose: Asks user for their favorite food, and tells # them it likes that food too. faveFood = raw_input("What is your favorite food? ") print "I love " + faveFood + " too!" What does this print out if the user enters 'Chocolate' when asked for their favorite food?

3 Classes and Objects Python is an object oriented programming language. All items of data are objects. Objects have properties: Things that describe the objects Objects have methods: Things an object can do. A class describes a group of objects that have the same methods and set of properties. Example: A car class Properties: color, number of doors, body type Methods: accelerate, brake, steer My car is an object that is a member of the car class.

4 Primitive Numeric Types TypeKind of infoUses integerwhole numberArithmetic expressions long integerLarge whole number " " floating point decimal number " " Examples: integer: long integer: L floating point:

5 Arithmetic Expressions with Floating Point Numbers Arithmetic operators for real numbers: +-*/** These work the way you would expect: * / **3.08.0

6 Arithmetic Expressions with Integers Arithmetic operators for integers: +-*/%** All work the way you would expect, except / and % DIV: Integer division truncates the decimal portion. 12 / 34 8 / 32 1 / 20 MOD: Gives the remainder of division of two integers: 7 % % 4 3

7 Example Using Numbers # Program: dogYears.py # Purpose: To calculate a dogs age in dogyears. ageOfDog = input("How old is the dog? ") dogYears = 7*ageOfDog print "The dog is", dogYears, "years old in dogyears."

8 Using commas vs. + in a print statement A + sign is used to concatenate (join) two strings. It can be used in a print statement to print two strings joined together. It cannot be used to join a string with a number. Example: myCat = "Calico" print "My cat is a " + myCat A comma is used to list items to print. It is used when we have several items of different types (e.g. a string and an integer) that we want to print. Example: myAge = 39 print "My age is", myAge

9 Strings A line of text is called a string. A string is indicated using quotes. Example: >>>"dog" 'dog' Triple quotes allow newlines in the middle of a string. Example: >>> ' ' 'This string has a break in the middle. ' ' ' 'This string has a break\nin the middle.'

10 String Methods Python provides a variety of operations with strings: Concatenation: +"dog" + "house" -> "doghouse" Repetition: *"cool"*3-> "coolcoolcool" Length: len(stringName)len("cool")-> 4 There are numerous other operations that can be applied to strings. Some of these are described in your textbook.