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what is **varkw in Python

Started by Lucidquiet Apr 8, 2006 at 2:44 PM 2 replies 1.8k views

Original Post

Apr 8, 2006 at 2:44 PM

The inspect.getargspec(func) returns a tuple of 4 things (args, varargs, varkw, and defaults). The arguments is just the names of the parameters; varargs the variable length arguments given to the function; and defaults is the default value any of the parameters... I've not found any explanation as to what varkw is, and what its for... I think I read that it might stand for var key words... I'm still looking though. But help is always appreciated, Thanks, L-

Fruny

Apr 8, 2006 at 2:55 PM

Consider a function defined as: def foo(a, b, c, *args).

When calling the function first three parameters will be placed in a, b, and c respectively. Any additional parameter will be stored in args as a list:

foo(1,2,3)       → a=1, b=2, c=3, args=[]foo(1,2,3,4,5,6) → a=1, b=2, c=3, args=[4,5,6]

Now consider a function defined as: def foo(a, b, c, **args).

args will gather "keyword arguments" in a dictionary:

foo(1,2,3)              → a=2, b=2, c=3, args = {}foo(1,2,3,n=3,u=42,z=6) → a=1, b=2, c=3, args = { 'n':3, 'u':42, 'z':6 }

Of course, if you have both *args and **kwargs in your parameter list, things get a bit more complicated, but that's the gist of it.

Fruny

Apr 8, 2006 at 2:57 PM

Note that there also is a symmetrical usage of * and ** that lets you pass a list or a dict respectively, and have them "expand" into the function's parameters.

def foo(a,b,c):    passm = [1,2,3]foo(*m)     # a=1, b=2, c=3n = {'a':1, 'b':2, 'c':3 }foo(**n)    # a=1, b=2, c=3

See here for details.

Lucidquiet

Apr 8, 2006 at 3:45 PM

Very cool, thanks a lot.

L-

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