Essentials of Python A Lunchtime Learning Guide is a book designed for individuals with programming experience, aiming to help them learn the fundamentals of Python efficiently in a short period. With the emergence of Generative AI, such as ChatGPT, the role of programming is undergoing a transformation. Previously, the ability to understand a language inside out and write code from scratch, known as output power, was considered the benchmark for programming proficiency. However, generative AI can now handle the 0 to 1 part of the process. Instead, humans need to focus more on input power, the ability to understand written source code, and analytical power, the ability to validate the code's validity. This book is tailored to this new programming style, aiming to help readers acquire the minimum knowledge required to get started with Python in the shortest possible time. The primary focus is on skimming through the source code, understanding the overall structure and connections, and grasping the program's behavior. This book aims to acquire the foundational knowledge for understanding the language, such as Python's basic syntax, data types, functions, classes, arrays, etc. The contents are written assuming a Python 3.10 environment. As of May 2024, the latest version is 3.12, but using too new a version may result in insufficient learning by generative AI or scarce information on the web, leading to reduced development efficiency, so a stable version with ample track record is used. Each chapter provides explanations using sample code to deepen practical understanding. Explanations of the execution results are also included to understand the behavior of the code.