Function / method parameters with * and ** in Python

In Python, you can define a function with optional parameters; if you specify a single * in front of a parameter, then that will be a tuple of all remaining unnamed values. And if you specify two *s in front of a parameter, that will be a dictionary of all remaining named parameters.

Let's see an example:

def demo(first, second, *third, **fourth):

  print "first",first

  print "second",second

  print "third",third

  print "fourth",fourth

  print

 

demo(1,2,3,4,5,6,7)

 

demo(5,6,7,8,aa=9,bb=11,cc=44)

When I run that, I get

C:\gje>python onetwo.py

first 1

second 2

third (3, 4, 5, 6, 7)

fourth {}

 

first 5

second 6

third (7, 8)

fourth {'aa': 9, 'cc': 44, 'bb': 11}

 

C:\gje>

Note that * and ** parameters must be the last parameters in a function definition, and if you're going to use both of them you put the ** at the very end, after the *.
(written 2007-04-04, updated 2007-04-03)

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