Variables and I/OTypesVariables and AssignmentSlide 4Slide 5Variable NamesExercisesOperatorsSlide 9PrecedenceAlternativesSlide 12StringsSlide 14Slide 15CompositionKeyboard InputSlide 18Slide 19Slide 20Variables and I/OTypes•Strings –Enclosed in quotation marks–“Hello, World!”•Integers –4, 3, 5, 65•Floats –4.5, 0.7•What about “56”?Variables and Assignment•A name that refers to a value•Python uses dynamic typingmy_num = 6my_string = “Hello”another_num = my_numVariables and Assignment•= often read as “gets the value”•my_num and another_num refer to the same objectmy_num = 6my_string = “Hello”another_num = my_num6“Hello”my_stringmy_numanother_numVariables and Assignment•Numbers and strings are immutablemy_num = 6my_string = “Hello”another_num = my_nummy_num = 7my_num = “CS”“Hello”my_stringmy_numanother_num76Variable Names•A combination of letters, digits, and _•Must begin with a letter•Case sensitive•OKAY–csiscool, my_variable variable2•NOT OKAY–cs is cool, 2ndvariable, print•Why not print?Exercises1. Assign the value 9 to the variable my_num2. Assign the value “17” to the variable my_string3. Print my_num+my_string4. What happens?5. Assign the value 17 to the variable my_string6. Print my_num+my_string7. What happens?8. Assign the value “print” to the variable print_var 9. What happens?Operators•You’ve seen +•-, *, /, ** (exponentiation)•% - remainder–12%6–12%5•What is the result of 5/2?Operators•What is the result of 5/2? 2•Why?–if both operands are integers, integer division is performed and the result must be an integer–result is truncatedPrecedence•PEMDAS –parentheses–exponents–multiplication–division–addition–subtraction•Evaluation done left to rightAlternatives•+=, -=, *=, /=•num += 3 -> num = num + 3Exercises1. Determine the results of the following:1. 5+9/4*3-22. (5+9)/(4*(3-2))3. 5**2+1/4-44. 5**(2+1)/(4-5)5. 5**(2+1)/(4-4)6. ((4-2)/(3-8)7. ((5+3)/3(2+1))Strings•Concatenation–print “Hello, “ + “World!”–print “Hello “ + “Class!” –print “Hello” + “Class!” •Repetition–print “Hello” * 3–print “Hello,” * 3Strings•Can be in single or double quotes–“hello” or ‘hello’•Escape sequences encode special characters–\n = newline, \t = tab, \\ = \, \” = “, \’ = ‘–can also use “ in string enclosed by ‘’ and ‘ in string enclosed by “”•“it’s fun”, ‘a “sample” string’•‘it\’s fun’, “a \”sample\” string”•http://docs.python.org/ref/strings.html–lists python escape sequencesExercises1. Execute the following statements:1. print “\tName: Bob”2. print “\t Name:\n Bob”3. print “Name:\a Bob”4. print “\a”*10Composition•What is the result of the following:age = 19print “Your age is “ + age•Instead, use ‘,’ to compose statementsage = 19print “Your age is “, ageKeyboard Input•input(<prompt>) reads an integer/float from the keyboard•raw_input(<prompt>) reads a string from the keyboard•Syntax–variable_name = input(<prompt>)–variable_name = raw_input(<prompt>)•Examples–mynum = input(“Enter number: “)–mystring = raw_input(“Enter string: “)Keyboard Input•Examplesmynum = input(“Enter number: “) same asprint “Enter number: “mynum = input()•Recall, an int can be a string, but a string cannot be an intExercises1. Write the algorithm for a program that prompts the user for two integers and displays the sum, difference, product, and quotient of the numbers.2. Write a program that implements the algorithm you wrote for exercise 1.Exercises3. Write the algorithm for a program that stores your name, age, street number, street name, city, state, and zip code in separate variables and the displays the data in the following format:My name is : Mickey MouseMy age is: 75My address is: 1234 Main Street, San Francisco, CA 941214. Write a program that implements the algorithm you wrote for exercise
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