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Python Programming Language
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*args and **kwargs
Ok, this is probably definitely a newbie question, but I have looked
all over the Python library reference material and tutorials which I
can find online and I cannot find a clear definition of what these are
and more importantly how to use them. From what I can tell from their
use in the examples I've seen, they are for passing a variable number
of arguments to a function (which I need to do in a program I am
working on). But how do you use them? Is there a fixed order in which
the arguments within *arg or **kwarg should be passed or will be
called within a function? I realize this probably involves a long-
winded answer to a very simple and common programming problem, so if
someone has a link to TFM, I'll gladly go RTFM. I just can't find it.
JonathanB wrote:
> Ok, this is probably definitely a newbie question, but I have looked
> all over the Python library reference material and tutorials which I
> can find online and I cannot find a clear definition of what these are
> and more importantly how to use them. From what I can tell from their
> use in the examples I've seen, they are for passing a variable number
> of arguments to a function (which I need to do in a program I am
> working on). But how do you use them? Is there a fixed order in which
> the arguments within *arg or **kwarg should be passed or will be
> called within a function? I realize this probably involves a long-
> winded answer to a very simple and common programming problem, so if
> someone has a link to TFM, I'll gladly go RTFM. I just can't find it.
That's because it's in the language reference, not in the library reference.
http://docs.python.org/ref/calls.html
Diez
"JonathanB" <doulo @gmail.com> wrote in message
> Ok, this is probably definitely a newbie question, but I have looked
> all over the Python library reference material and tutorials which I
> can find online and I cannot find a clear definition of what these are
> and more importantly how to use them. From what I can tell from their
> use in the examples I've seen, they are for passing a variable number
> of arguments to a function (which I need to do in a program I am
> working on). But how do you use them? Is there a fixed order in which
> the arguments within *arg or **kwarg should be passed or will be
> called within a function? I realize this probably involves a long-
> winded answer to a very simple and common programming problem, so if
> someone has a link to TFM, I'll gladly go RTFM. I just can't find it.
I hope this example code will help you understand:
>>> def a(*stuff):
print repr(stuff)
>>> def b(**stuff):
print repr(stuff)
>>> def c(*args, **kwargs):
print 'args', repr(args)
print 'kwargs', repr(kwargs)
>>> a(1,2,3)
(1, 2, 3)
>>> b(hello='world', lingo='python')
{'hello': 'world', 'lingo': 'python'}
>>> c(13,14,thenext=16,afterthat=17)
args (13, 14)
kwargs {'afterthat': 17, 'thenext': 16}
>>> args = [1,2,3,4]
>>> kwargs = {'no-way': 23, 'yet-anotherInvalid.name': 24}
>>> c(*args, **kwargs)
args (1, 2, 3, 4)
kwargs {'no-way': 23, 'yet-anotherInvalid.name': 24}
(sorry for the messed-up formatting)
JonathanB wrote:
> Ok, this is probably definitely a newbie question, but I have looked
> all over the Python library reference material and tutorials which I
> can find online and I cannot find a clear definition of what these are
> and more importantly how to use them. From what I can tell from their
> use in the examples I've seen, they are for passing a variable number
> of arguments to a function (which I need to do in a program I am
> working on). But how do you use them? Is there a fixed order in which
> the arguments within *arg or **kwarg should be passed or will be
> called within a function? I realize this probably involves a long-
> winded answer to a very simple and common programming problem, so if
> someone has a link to TFM, I'll gladly go RTFM. I just can't find it.
http://www.python.org/doc/faq/programming/#how-can-i-pass-optional-or...
(the first hit when you search python.org for *args and **kwargs)
Basically 'args' is a tuple with all the positional arguments, kwargs is
a dictionary with all the named arguments.
Likewise you can pass a tuple to a function like func(*tuple), or a dict
like func(**dictionary) or both, where the zuple has to come first.
> I hope this example code will help you understand:
>>Code Snipped<<
OOH!! That makes perfect sense, thanks!, *args are passed as a turple,
**kwargs are passed as a dictionary. That means **kwargs is probably
what I want.
JonathanB
On Jun 5, 7:31 am, "Diez B. Roggisch" <d@nospam.web.de> wrote:
> JonathanB wrote:
> > Ok, this is probably definitely a newbie question, but I have looked
> > all over the Python library reference material and tutorials which I
> > can find online and I cannot find a clear definition of what these are
> > and more importantly how to use them.
Also, well maybe op did not check THE tutorial. Or found explanation
too terse. But it's there.
http://docs.python.org/tut/node6.html#SECTION006600000000000000000
rd
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