>>> def f(a,b,c,d):  
...   print a,b,c,d  
...  
>>> args = (1,2,3,4)  
>>> f(**args)  
Traceback (most recent call last):  
  File "<stdin>", line 1, in <module>  
TypeError: f() argument after ** must be a mapping, not tuple  

>>> args = {'a':1,'b':2,'c':3}  
>>> args['d'] = 4  
>>> f(**args)  
1 2 3 4