newbie: prefix operator "**"

[Christian Jauvin]

Hello,

I am playing with some classes in the Tkinter module
to learn some GUI basics.

One problem is that I can't figure what is the meaning
of the prefix operator "**". I'm guessing that it has
something to do with dictionnaries, but I can't find
any explanation of it in the Python doc, nor on Google.

Here is a code snipped which I would like to understand:

class AnyWidget:

     def __init__(self, master=None, cnf=None, **kw):
         if cnf is None:
             cnf = {}
         if kw:
             cnf = _cnfmerge((cnf, kw))
         fcnf = {}

Thanks!