Force use of keyword arguments in method calls

[ahggns]

Method signatures are unstable due to a side effect of the implementation of #14. In order to prevent difficult to debug breaks we should force keyword arguments to be used.

This can be supported out of the box in Python 3:

def fun(*, arg1, arg2):
  pass

But we'll have to get creative for backcompat with Python 2:

def fun(*args, arg1, arg2):
   if args:
     raise ValueError("...")

@ferozco
cc @JacekLach, @jamding

[ferozco]

+1

I was actually in the process of writing up an RFC for something like this across languages