[jerf]

Python has always had Go-like interfaces in practice. The problem was that they were not reified into the code, so you had no easy way to know when calling a function and passing it a "file" exactly what file-like things the function was going to do with that "file" without reading the source code. You had to extract the interface yourself.

[fizzbatter]

Not only that, but there's simply no guarantees. You can abuse a function in any way you see fit in Python, and the only one that suffers is your runtime sever :(

Optional types in 3.5 look awesome - but i don't want to lose duck typing. I want Go-interfaces in Python.