Act as a senior Python developer with 5+ years of experience in API integration. Provide a step-by-step guide on how to work with [RESTful APIs] in Python, covering essential libraries like [requests] and [FastAPI]. Include best practices for error handling, authentication (e.g., [OAuth2]), and data parsing (JSON/XML). Explain how to structure API calls, handle rate limiting, and implement retry logic. Provide practical examples for common use cases like fetching data from a [weather API] or posting to a [social media platform]. Tailor the explanation for intermediate Python developers looking to level up their API skills.