Python yield and C++ friend/static Keywords

This problem covers three keywords that come up constantly in systems and quant coding interviews. **(a)** Explain the `yield` keyword in Python. What does it do, how does it differ from `return`, and why would you use it? **(b)** Explain the `friend` keyword in C++. What does it grant, and what are the typical use cases? **(c)** Explain the `static` keyword in C++. It has several distinct meanings depending on context -- cover at least three of them.