Guide to High School Computer Science
  • 💻Introduction
    • windows & Python Development
    • macOS & Python Development
    • Visual Studio Code Settings
    • Set up Github
    • Author Page
  • 🧠Prerequisite Skills
    • Keyboard Typing
    • Files & Directories
    • Use of Command Line
    • Git & GitHub
    • Markdown
    • Starting Your Python Project
  • 🐍Python Programming
    • 🍎Python Basics
      • What is Python?
      • Procedural Programming & Programming Paradigms
      • String Formatting
      • Data Types
      • Input & Output to Console
      • Working with Numbers
      • Useful Built-in Functions
      • Math & Random Module
      • Boolean Data Object
      • Comparison, Logical, and Membership Operators
      • If Statements
      • Binary Decisions
      • Multiple Decisions
      • Nested Conditions
      • [EXTRA] Bitwise Operators
      • [EXTRA] Python Style Guide
    • ⏮️Iterations
      • Introduction to While Loops
      • Infinite Loop
      • Controlling Your While Loops
      • Introduction to For Loops
      • For Loops w/ Numeric Sequences
      • For Loops w/ Strings & Lists
      • Iterable Functions w/ For Loops
    • 📦Collections
      • Strings
        • String Basics
        • String Indexing
        • String Slicing
        • String Operators & Functions
        • Basic String Methods
        • String Methods Extended
        • String Methods Document
      • Tuples & Lists
        • Tuples
        • List Basics
        • List are Mutable
        • Adding Items to a List
        • Removing Items from a List
        • Search & Reverse a List
        • List Comprehension
        • List Methods Document
      • Sets
      • Dictionary
      • How to Store Multiple Data Items
    • 💡Defining Functions
      • Functions
      • print() vs return
      • Pre-determined Arguments
      • Nested Functions
      • Map & Filter
      • [Extra] Dynamic Arguments
    • 💾File I/O
      • How to Save Text to an External File
      • Reading CSV in Python
      • Reading JSON in Python
    • 🔨Basic Python Projects
      • Basic Calculator
        • Improving the calculator
        • Exercise Set 1
        • Exercise Set 2
        • 💎Streamlit Application #1
      • Basic Password Generator
        • Exercise Set 3
        • Exercises Related to Math
        • 💎Streamlit Application #2
      • A To-Do Task List
    • ⏳Introduction to Algorithmic Thinking
      • Big-O Notation
      • Basic Algorithms
        • Linear Search
        • Binary Search
        • Basic Sorting Algorithms
      • Recursion
      • Brute Force Algorithms
      • Greedy Algorithm
        • Time on Task (CCC 2013 J4)
        • Dijkstra’s Algorithm
      • Divide and Conquer
        • Merge Sort
      • Dynamic Programming
    • 🤯Object Oriented Programming
      • Class & Objects (Definitions)
      • OOP in Python
      • Encapsulation
      • Polymorphism
      • Inheritance & Overriding
      • Override Magic Methods
      • Case Study: 2D Vectors
      • Case Study: Deck of Cards
      • Exercise
      • Abstract Data Types
      • Case Study: Static 1D Array From Java
    • Competitive Programming
      • Is This Sum Possible?
        • Is the dataset sorted?
        • Searching for a value
        • Determine if the difference between an integer from the array and the target value exists
        • Sorting Algorithms
        • Using Two Pointers
      • Two Sum - LeetCode
        • Generate all possible pairs of values
        • Subtract each value from the target, see if the difference exists in the list
      • Longest Common Prefix - LeetCode
        • Compare all possible prefixes
        • Create the longest common prefix with the direct neighbour
      • Length of Last Word - LeetCode
        • Compare all possible prefixes
      • Where can I go from one point to another?
      • Sample Outline
    • IB Recipe Book
  • 💾Python & Databases
    • Intro to Databases & Data Modeling
      • Common Data Types in SQL
      • Introduction to ERDs
      • Primary Keys and Foreign Keys
      • Database Normalization
    • What is SQL?
      • Getting Started
      • SELECT Queries
        • Selection with Conditions
        • Selection with Fuzziness
        • Selection and Sorting in Order
        • Selection without Duplicates
        • Selection with Limited Number of Outputs
      • AGGREGATE Queries
        • Counting Rows
        • Sum, Average, Min/Max Queries
        • Working with Aggregate Queries
        • Power of using Groups
        • Exercise
      • Interacting with Multiple Table
      • Inserting Data
      • External Resource
  • ☕Java Essentials
    • Basics
      • Starting Java
      • Data & Variables
      • Handling User Inputs & Type Conversion
      • Arithmetic
      • IPO Model
      • Basic Built-in Methods
      • Exercise Questions
    • Conditionals
      • Boolean Operators
      • Compare Strings
      • If Statements
      • If Else Statements
      • Making Multiple Decisions
      • Using Switch
      • Flowchart Symbols
      • Exercise Questions
    • Iterations
      • While Loops
      • For Loop
      • Exercises
    • Java Type Casting
    • Strings
      • Common String Practices
      • String Formatting
      • Java Special Characters
    • Collection
      • Arrays
      • For Each Loop
      • ArrayList
      • Exercise Questions
    • Static Methods
      • (Aside) Clearing your Console
    • Randomness in Java
    • Delayed Output in Java
    • Java Output Formatting
    • Java Style Guide
  • 🛠️JavaScript Programming
    • Our Programming Editor & Workflow
      • Hello, world!
      • Commenting & Variables
      • Data in JavaScript
      • Operators
      • String Formatting
      • Getting User Input
    • JavaScript Exercise Set 1
    • Making Decisions
      • Comparing Values
      • Combining Boolean Comparisons
      • Creating Branches
    • JavaScript Exercise Set 2
    • While Loops
      • Infinite While Loop
      • While Loops and Numbers
      • While Loops and Flags
      • While loops w/ Strings
    • JavaScript Exercise Set 3
    • Subprograms & Functions
      • Creating a Function in JavaScript
      • Function with Input and Assignable Output
    • JavaScript Exercise Set 4
  • 💾Topics in CS
    • Computer Environments & Systems
      • Computer Components
        • In-depth Explanations
      • File Maintenance
      • Computer & Safety
      • Software Development
      • Bits & Binary
    • Careers related to Computer Science
    • Postsecondary Opportunities
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  1. Python Programming
  2. Collections
  3. Tuples & Lists

List are Mutable

Lists are mutable data type. This means that its composition can be altered without recreation, reassignment, redeclaration. This can be dangerous for most new programmers.

Example 1: Altering via index:

# Manipulation by index

primes = [2,3,5,7,11]
print('primes currently:', primes)
primes[1] = 10000
primes[2] = 'Hello!'

print('primes now:', primes)
primes currently: [2, 3, 5, 7, 11]
primes now: [2, 10000, 'Hello!', 7, 11]

In example 1, you can see that we can change the composition of the list without redeclaring a new list for the variable: primes.

Example 2: Copying a List to another variable:

# Copying a list to a new variable

primes1 = [2,3,5,7,11]
primes2 = primes1
print('primes1 currently:', primes1)
print('primes2 currently:', primes2)

primes2[-1] = 13

print('primes1 now:', primes1)
print('primes2 now:', primes2)
primes1 currently: [2, 3, 5, 7, 11]
primes2 currently: [2, 3, 5, 7, 11]
primes1 now: [2, 3, 5, 7, 13]
primes2 now: [2, 3, 5, 7, 13]

In example 2, we have only manipulated the list called primes2. However, the original list called primes1 was also affected by the changes as well.

This is because when a new variable is created to hold another list variable. Python saves memory by pointing towards where the original list is located rather than creating a whole new copy.

Therefore, any changes will affect both variables.

Solution: Use a method called .copy()

This method will help us create a new list in memory with the same values from the original.

# Using .copy() method

primes1 = [2,3,5,7,11]
primes2 = primes1.copy()
print('primes1 currently:', primes1)
print('primes2 currently:', primes2)

primes2[-1] = 13

print('primes1 now:', primes1)
print('primes2 now:', primes2)
primes1 currently: [2, 3, 5, 7, 11]
primes2 currently: [2, 3, 5, 7, 11]
primes1 now: [2, 3, 5, 7, 11]
primes2 now: [2, 3, 5, 7, 13]

Example 3: Sorting & List Methods

List has a built-in method to help sort. Unlike the sorted() function, list has a method which allows us to manipulate the list you are sorting without creating a whole new variable.

# List. sort() method

a_list = list('Hello, World!')
print('a_list now:', a_list)

a_list.sort()

print('a_list sorted:', a_list)
a_list now: ['H', 'e', 'l', 'l', 'o', ',', ' ', 'W', 'o', 'r', 'l', 'd', '!']
a_list sorted: [' ', '!', ',', 'H', 'W', 'd', 'e', 'l', 'l', 'l', 'o', 'o', 'r']

Examine that there is no assignment operation occurring to help us sort. We are using a method that lists have to just manipulate the given list rather than needing to create a new container like strings.

Below are the list of methods that affect the composition of a list. They will not require recreation/reassignment.

  • append()

  • extend()

  • insert()

  • remove()

  • pop()

  • sort()

  • reverse()

PreviousList BasicsNextAdding Items to a List

Last updated 10 months ago

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