Lecture Notes for CPSC 121 (Fall 2012) - Slices and Boolean Values, Study notes of Computer Science

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Today ...

• Slices (cont.)
• Boolean values

Homework

• HW 8 due
• HW 9 out

Slices always return new (shallow copied) lists

list3 = [’a’, [’b’, ’c’], ’d’]

list4 = list3[1:3]

list [[’b’, ’c’], ’d’]

list4[0][1] = ’e’

list [[’b’, ’e’], ’d’]

list [’a’, [’b’, ’e’], ’d’]

This is also true of list concatenation

list5 = [1, [10, 100]]

list6 = list5 + [2]

list [1, [10, 100], 2]

list5[1][0] = 50

list [1, [50, 100]]

list [1, [50, 100], 2]

List Slice Exercises

Assume that:

my_str = "go bulldogs"

Define expressions that Use slices to generate the following strings:

1. "go"
2. "bulldogs"
3. "bull"
4. "dog"
5. "gu"
6. "bulldogs go"
7. "bull-dogs"

Boolean values

What is a Boolean value?

• A value representing either true or false
• After George Boole (logician that invented Boolean logic, circa 1847)

Python has special Boolean values

• True represents true
• False represents false
• Both are of type bool

type(True) <class ’bool’>

type(False) <class ’bool’>

A detail of Python bool values

• bool is a special type of int
• You can think of True as 1 and False as 0