Python Type Checking
Promises is a little Python toolkit for maintaining some sanity when doing testing or building an API in dynamically typed languages. Easily declare the signature of your functions like so:
from promises import accepts, rejects @accepts(int) @rejects(int) def f(x): return x+1
Promises only exposes a very minimal declarative and decorator-based API that is inspired by function signatures in Go, and is very easy to learn. You can get more documentation of the project by visiting github.com/eugene-eeo/promises.