Unformatted text preview: 10/6/2008 The if statement dissected
Look Look at its separate parts: ECS 10
10/6 if name == ‘’ : name = ‘Anonymous’
if if is a Python commands ‘’ ‘’ and ‘Anonymous’ are strings Test Test  name == ‘’ is actually an expression – ‘’a new kind… Boolean Boolean expressions
Values Values of Boolean expressions are either True or False Boolean Boolean is a new data type. We now have four data types (and four kinds of of expressions): integer, floating point, string and Boolean. Boolean expressions
Have Have value True or False True False Examples: Examples:
answer == ‘R’ x < 30 30 2+2 == 4 2+2 <= 5 ‘cat’ != ‘Cat’ not equals Boolean algebra
Named Named after George Boole (18151864) (1815Main Main idea: you can write down logic as mathematical formulas, as well as in sentences. His His book: An Investigation An into the Laws of Thought Computers Computers do logical as well as numerical and string computation. True True and False
These These are the only two possible Boolean data items. NOT NOT descriptions of expressions; actual data. Maybe better names would be Truth and Falsehood, Falsehood, so we think of them as things. things We We can not only store True and False in variables, we can compute with them. 1 10/6/2008 and and or
and and and or are the operators on Boolean data >>> 5+6 11 >>> (2<3) and (1<3) True Boolean, Boolean, operator, Boolean – resulting data is Boolean or
>>> True or True True >>> True or False True >>> False or True True >>> False or False False Memorize this! this! Use to check input
or or operator: Converting types
int('5')/2
Converts the string ‘5’ to the integer 5 to if (reply == ‘D’) or (reply == ‘R’):
and and operator: if (reply != ‘D’) and (reply != ‘R’): Converting Data
Convert Convert an integer to a string: x = str(10) x is the string ‘10’ is y = float(‘8.3333’) y is the floating point number 8.3333 Getting numbers from the user
reply = raw_input(‘Feet: ‘) feet = int(reply) reply = raw_input(‘Inches: ‘) inches = int(reply) Notice we use the variable reply twice. When we put the second string into reply, the first one gets written over. It’s gone! 2 10/6/2008 Body mass index
Kilograms / (meters2)
Or, Or, in `English Imperial Units’ Yao Ming (Pounds * 703) / (inches2)
25 25 or greater is overweight. 7 feet, 6 inches. 310 pounds. 3 ...
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 Winter '07
 Amenta
 Logic, Imperial units, George Boole, False Boolean Boolean

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