Lecture Notes for CPSC 121 Fall 2012: Exam 2 Overview and List Slices, Study notes of Computer Science

Download Lecture Notes for CPSC 121 Fall 2012: Exam 2 Overview and List Slices and more Study notes Computer Science in PDF only on Docsity!

Today ...

• Exam 2 overview
• Slices

Reminder

• Exam 2 (wed.)

Exam 2 Overview

Basics

• 10% of final grade
• ≈ 6 questions
• closed book & notes

Topics

• fruitful functions (return statement)
• input function
• type conversion functions (int, float, etc.)
• lists
• string and list operations (+, *, [], etc.)
• for loops
• range function
• slices (today)

List slices

A slice is a sublist (or substring)

The slice operator [i:j] returns subsequences

• The subsequence starts at index i and ends at j-1 (or len-1)
• Omitting the first index starts the slice at index 0
• Omitting the last index makes the slice go to (and include) the last value

a_list = [10, 20, 30, 40, 50]

a_list[0:5] [10, 20, 30, 40, 50]

a_list[1:4] [20, 30, 40]

a_list[2:3] [30]

a_list[2:2] []

a_list[:4] [10, 20, 30, 40]

a_list[2:] [30, 40, 50]

a_list[0:-1] [10, 20, 30, 40, 50]

a_list[0:200] [10, 20, 30, 40, 50]

a_list[-1:10]

a_list[:] [10, 20, 30, 40, 50]

a list[:] does a “shallow” copy of the list

• What do you think this means?

An example:

list1 = [’python’, ’is’, [’fun’, ’easy’]]

list2 = list1[:]

list [’python’, ’is’, [’fun’, ’easy’]]

list [’python’, ’is’, [’fun’, ’easy’]]

list2[2][1] = ’hard’

list [’python’, ’is’, [’fun’, ’hard’]]

list [’python’, ’is’, [’fun’, ’hard’]]