Python method/function arguments starting with asterisk and dual asterisk [duplicate]

Question

I am not able understand where does these type of functions are used and how differently these arguments work from the normal arguments. I have encountered them many time but never got chance to understand them properly.

Ex:

def method(self, *links, **locks):
    #some foo
    #some bar
    return

I know i could have search the documentation but i have no idea what to search for.

Ditto--here is a link that will help: saltycrane.com/blog/2008/01/… — user798719
– user798719, Commented Mar 14, 2013 at 21:49
"I know i could have search the documentation but i have no idea what to search for." Happens all too often when learning. it would have been like saying "what's that thing in the stuff?" What some so-called "experts" forget is that sometimes tere's a minimum level of understanding require to know how the hell to ask a question. — monsto
– monsto, Commented Apr 10, 2014 at 20:24
You could be interested to read also one of the questions What does ** (double star) and * (star) do for Python parameters? or What does asterisk * mean in Python? — strpeter
– strpeter, Commented Sep 21, 2015 at 17:52

user · Accepted Answer · 2017-10-07 04:29:12Z

125

The *args and **keywordargs forms are used for passing lists of arguments and dictionaries of arguments, respectively. So if I had a function like this:

def printlist(*args):
    for x in args:
        print(x)

I could call it like this:

printlist(1, 2, 3, 4, 5)  # or as many more arguments as I'd like

For this

def printdict(**kwargs):
    print(repr(kwargs))

printdict(john=10, jill=12, david=15)

*args behaves like a list, and **keywordargs behaves like a dictionary, but you don't have to explicitly pass a list or a dict to the function.

See this for more examples.

edited Oct 7, 2017 at 4:29

user

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answered Nov 29, 2010 at 18:03

Rafe Kettler

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4 Comments

User Over a year ago

But can you explicitly pass a list or dict to the function?

Elvis Teixeira Over a year ago

Yes, you can. The list will be args[0] if you pass it "as is". In the other hand, f you call the function with an asterisk (not the one in the function definition, this is in the call) then, the passed list will BE THE actual args tuple.

AljoSt Over a year ago

*args is a tuple, not a list

Jack Peng Over a year ago

>>> def d(*args): ... print(type(args)) >>> d(1, 2, 3) <type 'tuple'>

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