What does ** and * do for python parameters?

The *args and **kwargs ist a common idiom to allow arbitrary number of arguments to functions as described in the section more on defining functions in the the python documentation.

The *args will give you all funtion parameters a a list:

In [1]: def foo(*args):
   ...:     for a in args:
   ...:         print a
   ...:         
   ...:         

In [2]: foo(1)
1


In [4]: foo(1,2,3)
1
2
3

The **kwargs will give you all keyword arguments except for those corresponding to a formal parameter as a dictionary.

In [5]: def bar(**kwargs):
   ...:     for a in kwargs:
   ...:         print a, kwargs[a]
   ...:         
   ...:         

In [6]: bar(name="one", age=27)
age 27
name one