+- Python Forum (https://python-forum.io)
+-- Forum: General (https://python-forum.io/forum-1.html)
+--- Forum: News and Discussions (https://python-forum.io/forum-31.html)
+--- Thread: what is ,*, ? (/thread-4791.html)
what is ,*, ? - Skaperen - Sep-09-2017
in the documentation The Python Library Reference (at least in the PDF copy) many functions and class methods are shown with an argument list that has
,*, in it. what does that mean?
RE: what is ,*, ? - metulburr - Sep-09-2017
do you mean variable arguments such as...
def func(*args)or
def func(**kwargs)?
RE: what is ,*, ? - ichabod801 - Sep-09-2017
No, he means
,*,. Check out the documentation for sorted. It uses that notation. I haven't figured out what it means yet.
RE: what is ,*, ? - Skaperen - Sep-09-2017
a little while ago i was looking at the document for os.stat() and it also has
,*, shown. i played around with it by adding an extra argument, but with 2 arguments it objected and said that 2 arguments is too many. i then tried spliting the path into parts and gave it a list but it didn't like that, either. google gives me no matches for it.
RE: what is ,*, ? - hbknjr - Sep-09-2017
I always thought
* was for unpacking, but that's surely not the case here.I looked at sorted function code didn't find any use of
*(except for the pointers in C).May be it is to differentiate positional or keyword arguments.
func(positional args,*, keyword args)may be to represent that after
,*, no positional argument could be there.Just a theory, let me know if you find a counter-example.
Ok so i tried to use
,*, in function defination and all it did is convert the argument on right to keyword argument.>>> def myFunction(a, *, b): ... return a+b ... >>> myFunction(3,5) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: myFunction() takes 1 positional argument but 2 were given >>> myFunction(3,b=5) 8
RE: what is ,*, ? - syogun - Sep-09-2017
This
'*' specifies an argument that can be supplied only by keyword.Quote:keyword-only: specifies an argument that can be supplied only by keyword. Keyword-only parameters can be defined by including a single var-positional parameter or bare * in the parameter list of the function definition before them, for example kw_only1 and kw_only2 in the following:
def func(arg, *, kw_only1, kw_only2): ...
RE: what is ,*, ? - metulburr - Sep-09-2017
Good to know.
Im not sure when i would use that. kwargs were always the last parameters given. And ifi wanted to signify that it was indeed kwargs, i would put a param=None or something.
RE: what is ,*, ? - dvs1 - Sep-09-2017
def test(a, b='test'):
print(a)
print(b)
def test2(a, *, b='test'):
print(a)
print(b)
test('hello', 'world')
test2('hello', b='world')If you write: test2('hello', 'world')you get: TypeError: test2() takes 1 positional argument but 2 were given
https://www.python.org/dev/peps/pep-3102/
RE: what is ,*, ? - Larz60+ - Sep-09-2017
It looks like the name of the function is automatically passed as argument b:
>>> def test2(a, *, b='test'):
... print(a)
... print(b)
...
>>> test2('hello')result:Output:hello
test
>>>RE: what is ,*, ? - Skaperen - Sep-10-2017
(Sep-09-2017, 12:26 PM)syogun Wrote: Thisso, where'*'specifies an argument that can be supplied only by keyword.
Quote:keyword-only: specifies an argument that can be supplied only by keyword. Keyword-only parameters can be defined by including a single var-positional parameter or bare*in the parameter list of the function definition before them, for example kw_only1 and kw_only2 in the following:def func(arg, *, kw_only1, kw_only2): ...
,*, is not used, the documentation is saying that these arguments, or those before the ,*,, can be provided by either a named option or be unnamed in the position shown?so, is this how to code a function prototype to do that?
def f(positional, either_way_with_default_value='foo', *, only_as_a_named_option='bar'): ...???
so how can a definition of an argument specifying that it can be given either way define the difference between a required argument and one that is not required (e.g. calling f() above with just one positional argument)?