python: non-defined function arguments

You know that you can get named arguments of the routine that are not in function definition with **kw parameter:

def func(**kw):
     for k,v in kw.items(): print "%s: %s" % (k,v)

kw is a dict here where key is parameter name and value is parameter value. So if you call

func(a=1, b=2)

your kw will be

{'a': 1, 'b': 2}

>>> func(a=1, b=2)
a: 1
b: 2

The same is for the unnamed arguments:

def func(*a):
     for v in a: print v

a is a list of arguments here

func(1, 2)

will produce tuple a

(1, 2)

>>> func(1, 2)
(1, 2)

Nice I should say. Let's view the other side. You have function

def func(a=1, b=2):
     print a, b

and you have a dict

kw = {'a': 3, 'b': 4}

Now you just can use some py magic

func(**kw)

You will get a=3 and b=4:

func(**kw)
3 4

And for the unnamed arguments

def func(a, b):
     print a, b

If you define a list of 2 values

a = (1, 2)

and pass it to the func

func(*a)

you will get a=1 and b=2

func(*a)
1 2

Some extra py magic for these tricks:

def func(a=1, b=2): pass
func(**{'a': 3, 'b': 4})

def func(a, b): pass
func(*(1, 2))