Function params with **? what do these mean?

[Larry Bates]

J Rice wrote:
> I'm sorry for such a basic question, but I haven't been able to phrase
> a search that gets me an answer and my books are totally silent on
> this.  I have seen a number of python function defs that take
> parameters of the form (**param1).  Looks like a pointer... but my
> books on python (basic as they are) don't make a mention.  What is
> this?
> 
> Jeff
> 
There are too forms that you may be confusing.  First

>>> def foo(x,y,z):
>>>     return x+y+z

>>> t=[1,2,3]

>>> foo(*t)

6


This tells python to expand t and pass it as as 3
separate arguments

The second is:

>>> def foo(*args):
>>>    return sum(args)

>>> foo(1,2,3)

6

This allows you to treat all the arguments to a function
as a list of arguments no matter how many there are.

or

>>> def bar(**kwargs):
>>>    for key, value in kwargs.items():
>>>        print "key=%s, value=%s" % (key, value)
>>>    return

>>> bar(a=1, b=2, c="this is a test")
key=a, value=1
key=c, value=this is a test
key=b, value=2


This allows you to access keyword arguments via a dictionary
in the function, instead of individually.


You can combine these to make very powerful functions/methods
that can handle different numbers of arguments and keyword
arguments.

def foo(*args, **kwargs):
...


Larry Bates