The API related to a software library describes and prescribes (provides instructions on how to use it) how each of its elements should behave, including the most common error scenarios. The behavior and interfaces of the API is usually referred to as library specification, while the library is the implementation of the rules described in such specification. Libraries and frameworks are usually language bound, but there are some tools that make it possible to use a library in a different language. You can use C code in Go using CGO, and in Python you can use CPython.