Python is a favored language for developing chat applications due to its simplicity, readability, and the availability of numerous libraries and frameworks like Flask and Django, which streamline the development process. The language's ease of use makes it accessible for beginners, and its versatility is enhanced by a robust community offering resources and support. Integrating PubNub's real-time chat API with Python allows developers to implement real-time messaging and presence capabilities, creating scalable and robust chat applications. However, Python's limitations, such as the Global Interpreter Lock (GIL) affecting concurrency and potential performance issues due to its speed, require developers to employ efficient libraries and optimize code. Building a chat application involves setting up the development environment, selecting suitable frameworks, designing the frontend and backend, and integrating real-time messaging features like PubNub, which provides low-latency publish-subscribe messaging and presence detection. Developers must also address challenges related to scalability and performance, such as handling large-scale connections and ensuring message delivery during network disruptions, by incorporating load balancing and persistent storage mechanisms.