Contents Welcome 1 Read a Children''s Book Problem Solving, in General Problem Solving, in Detail Our First Computational Problem Imagine a Specific Instance Sketch Using Computational Thinking Capturing This Thinking An Environment for Coding Our Generic IDE Our First Pseudocode Comments Commands and Input Parameters Scripts versus Execution Our First Error The Interactive Interpreter Code and Transcript Blocks Interacting with the Interpreter The Interpreter as a Calculator Python Help Revisiting Our First Error Undefined Names Talking through Your Confusion Naming a Computation''s Result Debugging Showtime Printing to the Console Pane Statements, Objects, Attributes, and Types Namespaces Strings and String Literals Variables Valid Names in Python Terminology Illustrated Aliasing Reading Two Lines Carriage Returns Reading an Entire Story Creating a Loop End of File (EOF) Three Major Tasks Testing a Condition Exiting the Loop Indentation Loop Until Any Book This Problem, in General Historical References to Computational Thinking 2 Grab the Dialogue What Is the Current Task? A New Problem Splitting the Problem Into Small Pieces Reuse Switching between Goals Finite State Machines Error Handling in FSMs Encoding the state information This or That Work on a State Strings as a Sequence of Characters Membership Test Coding a Transition Indexing and Slicing For-Loops String Find Design Patterns for Error Handling Never Go Too Long without Testing Concatenation, Overloading, and Shorthands Off-by-One and Other Potential Errors Testing Beware of Hidden Assumptions Function Composition Abstraction as Information Hiding There Is No Character 3 Replace Text with Emoji Internationalization Encoding Standards Unicode A New Problem Decomposition to Reduce the Problem''s Complexity Strings as Immutable Sequences Encode an Emoji in Unicode Multiple Different Replacements Feeling Overwhelmed? Functions Function Definitions The Actual Function Definition and Its Invocation Function Execution Abstraction, Decomposition, and Algorithms Definition Before Use Python''s Special Variables Docstrings Getting a Feel for Abstraction Another Kind of Abstraction Lists Are Sequence Objects Abstraction Barriers Methods Modules Revisiting ''_main_'' Pure Functions 4 Query a Web Resource Packages and Libraries APIs A New Problem Searching Wikipedia The Client-Server Programming Model Resources, Transactions, and Protocols The URL The Programmable Web Python Dictionaries An HTTP Response The Response Header JSON and the Response Body Enumerating Answers for HOLLIS Beyond Printing Blocking and Non-blocking Function Calls 5 Play Guess-a-Number Guessing a Number The Player''s Guess Type Conversion Try and Recover The Game Loop Testing Our Proposed Solution A Networked Architecture Its Sequence Diagram When to Use a New Library Sockets in Action Specifying the Other Party Sending and Receiving Messages Size Matters Encoding Again! A Simplified Networking Interface The Server A Connection Picking Up a Call The Conversation Programmer Beware Run It! 6 Do You See My Dog? Numbers and Knowledge Do You See My Dog? No Interpretation, Please Reading a Hexdump Hexadecimal Explained Converting between Number Systems Does the Computer See My Dog? Painting a Picture Bits One Finger, No Thumb The Digital Abstraction Bits, Bytes, and Nibbles Setting a Pixel''s Color Saturation Overflow and Underflow Finding Edges 7 Many but Not Any Number Floating-Point Numbers and numerical Computing Computers Struggle with Arithmetic? The Range of a FP Number Precision Illustrating This Issue for Precision Getting Started One Bit at a Time Searching for the Smallest Difference FP Errors Accumulate 8 What Is My Problem? Data Science Images as Data about the World Yes, You Must Clean Up Understanding What Might Go Wrong Noise and Its Removal The Power to Create New Realities A Process for Eliminating Photobombing This Data Is Wrong, but. Zero Out the Unnecessary Details No Visible Difference Image Steganography Where Is That Pixel? And How Did We Get There? Visualizing a Traversal Inverting a Pixel''s Color Naming the Traversal Specifying the Range You Want Storing a 2D Array in Memory End of Act I 9 Find a Phrase A Complex Problem-to-Be-Solved Some Basic Facts Which Algorithm? Algorithms, Formally A Well-Studied Specification for String Matching Is a Specification an Algorithm? A Brute-Force Algorithm A BF-String-Matching Program One Algorithm, Multiple Implementations Evaluation Evaluation in Context Measuring Performance How Do We Do Better? Loops Are Where the Action Is Computational Complexity Computational Complexity in Action Problem Unsolved 10 Build an Index Strings to Numbers A Simple Hash Function Updating a Hash with O(1) Work Allow Collisions Other Applications of Hashing Indices for Fast Data Retrieval Hash Tables The Speed of Array-Index Operations With High Probability Collision Resolution Specification for Creating a Book Index Building Top-Down Updating the Index Sort and Strip 11 Discover Driving Directions A New Approach to Programming Driving Directions, a Formal Specification Parallels with Finite State Machines Solutions with Specific Characteristics Let''s Walk Before We Drive A Random Walk Will It Work? A Short Walk, Please No Loops Only Visit New Spots A Dog Walk Simulation To Maps through OO Programming Classes Building an Instance Self and Instance Attributes Methods Representation Invariant Magic Methods Building on Others General Maps Keeping Track Remembering How We Got There The Solution Depth-First Search (DFS) Breadth-First Search (BFS) Informed Searches 12 Divide and Conquer A Specification for Sorting Sorting in Python Sorting in Descending Order Sorting with Your Own Comparison Function Sorting Playing Cards Time Complexity of Brute-Force Sorting Binary Search Divide and Conquer From Split to Merge Iterative Merge Sort Recursion Iterative Factorial Recursive Merge Sort Beckett''s Challenge Its Base Case The Play with a Single Actor Looking for the Pattern A Polished, Full Solution 13 Rewrite the Error Message The Mistakes We Make in Problem Solving Our Problem-to-Be-Solved From the GUI to the Shell Understanding Paths From Paths to Programs Redirecting Inputs and Outputs Which Output? Pattern Matching Wildcards in the Shell Regular Expressions Finding Simple Words Matching Metacharacters Using Res Finding Filenames Python RE Extensions Putting It All Together Shell Pipes Scripting What the Shell Did Concurrency Making python32 Look Like python3 14 The Dream of Bug Fixing Finding All Bugs Decision Problems Uncomputable Problems An Analysis That Finds a Bug Running Our Simple Analysis A Tool for Running Analyses Grabbing a Function with a Syntax Error Analyzing Other Functions Using s A Non-trivial Decision Problem An Indecisive Decision Function Insight from Indecision Specifications without Implementations 15 Embrace Runtime Debugging The Duality of Code and Data Breakpoints and Runtime State Inserting a Breakpoint Inserting a New Statement Indenting That Statement Launching a Script from Another Instrumenting a Script REPL 16 Catch Them Early Divide-by-Zero Bugs A Silly Coding Error What''s Hidden Why Compile? Finding Type Errors To Squiggle or Not Dynamic Typing Why Types Are Interesting Types versus Values Dynamic Type Checking Static Type Checking Type Hints No Free Lunch 17 Build Prediction Models Predicting Home Prices Your Sister''s Data Solving This Problem Ourselves Machine Learning Labeled Training Data ML Workflow Getting a Feel for the Data Set the Prediction Target Pick Some Features Fit the Model to Our Data Predicting Unseen Data Model Validation Making the Fit Just Right Bias in ML Classifying Comments as Toxic More Art Than Science 18 Use Generative AI Navigating the Jagged Frontier My Use of GAI Large Language Models (LLMs) The Operation of LLMs Complexity for Simplicity T.