The most efficient way to build a loop in Python, in terms of computing complexity, is to use a for loop with the range() function. This is because the range() function generates a sequence of numbers that can be easily iterated over by the loop, without the overhead of creating a list or other data structure.

Regarding promising languages for the near future, it's difficult to predict with certainty. However, some languages that are currently gaining popularity and are likely to continue to be in demand in the next 5 years include:
1. Python: Python is a versatile language that is widely used in a variety of industries, including data science, machine learning, and web development.
2. JavaScript: JavaScript is the language of the web and is essential for front-end web development, as well as back-end development with frameworks like Node.js.
3. Rust: Rust is a systems programming language that emphasizes speed, security, and memory safety. It's gaining popularity for its ability to write low-level code that's both fast and safe.
4. Go: Go is a language developed by Google that's designed for concurrency and scalability. It's increasingly being used for building microservices and other distributed systems.
5. Kotlin: Kotlin is a modern language that's gaining popularity for Android app development. It's interoperable with Java, making it easy to integrate into existing Java projects.
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