* in Python

[placid]

Hi all,

Can someone tell me what * in the following code means/does a Google
search didnt turn up anything as i dont know what the * is called
(related to Python and i dont think Python has pointers)

def test(*args):
pass

and sometimes its;

def test(**args):
pass


Cheers

[Fredrik Lundh]

Re: * in Python

placid wrote:
[color=blue]
> Can someone tell me what * in the following code means/does a Google
> search didnt turn up anything as i dont know what the * is called[/color]

see sections 4.7.2 and 4.7.3 in the tutorial:

http://docs.python.org/tut/node6.html#SECTION006740000000000000000

for more details, see the description of the "def" statement in the
language reference.

</F>

[Duncan Booth]

Re: * in Python

placid wrote:
[color=blue]
> Hi all,
>
> Can someone tell me what * in the following code means/does a Google
> search didnt turn up anything as i dont know what the * is called
> (related to Python and i dont think Python has pointers)
>[/color]
* is for variable number of positional arguments, ** is for variable
keyword arguments. The syntax is symmetrical when defining functions and
when calling them.

See http://docs.python.org/ref/calls.html
and http://docs.python.org/ref/function.html

[placid]

Re: * in Python


Duncan Booth wrote:[color=blue]
> placid wrote:
>[color=green]
> > Hi all,
> >
> > Can someone tell me what * in the following code means/does a Google
> > search didnt turn up anything as i dont know what the * is called
> > (related to Python and i dont think Python has pointers)
> >[/color]
> * is for variable number of positional arguments, ** is for variable
> keyword arguments. The syntax is symmetrical when defining functions and
> when calling them.
>
> See http://docs.python.org/ref/calls.html
> and http://docs.python.org/ref/function.html[/color]

so * basically means that args is a list containing more arguments that
can change in size, whereas ** means that args is a dictionary of
key=value arguments?

[Bruno Desthuilliers]

Re: * in Python

placid wrote:[color=blue]
> Duncan Booth wrote:
>[color=green]
>>placid wrote:
>>
>>[color=darkred]
>>>Hi all,
>>>
>>>Can someone tell me what * in the following code means/does a Google
>>>search didnt turn up anything as i dont know what the * is called
>>>(related to Python and i dont think Python has pointers)
>>>[/color]
>>
>>* is for variable number of positional arguments, ** is for variable
>>keyword arguments. The syntax is symmetrical when defining functions and
>>when calling them.
>>
>>See http://docs.python.org/ref/calls.html
>>and http://docs.python.org/ref/function.html[/color]
>
>
> so * basically means that args is a list[/color]

A tuple IIRC
[color=blue]
> containing more arguments that
> can change in size, whereas ** means that args is a dictionary of
> key=value arguments?
>[/color]

Why don't you try by yourself in the Python shell ? One of the nice
things with Python is that it's quite easy to explore and experiment.


--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[Duncan Booth]

Re: * in Python

Bruno Desthuilliers wrote:
[color=blue][color=green]
>> so * basically means that args is a list[/color]
>
> A tuple IIRC[/color]

In a function definition * means that any remaining position arguments will
be passed in as a tuple. In a function call the * means that any sequence
will be unpacked as positional arguments: it doesn't have to be a list or
a tuple.

[placid]

Re: * in Python


Bruno Desthuilliers wrote:[color=blue]
> placid wrote:[color=green]
> > Duncan Booth wrote:
> >[color=darkred]
> >>placid wrote:
> >>
> >>
> >>>Hi all,
> >>>
> >>>Can someone tell me what * in the following code means/does a Google
> >>>search didnt turn up anything as i dont know what the * is called
> >>>(related to Python and i dont think Python has pointers)
> >>>
> >>
> >>* is for variable number of positional arguments, ** is for variable
> >>keyword arguments. The syntax is symmetrical when defining functions and
> >>when calling them.
> >>
> >>See http://docs.python.org/ref/calls.html
> >>and http://docs.python.org/ref/function.html[/color]
> >
> >
> > so * basically means that args is a list[/color]
>
> A tuple IIRC
>[color=green]
> > containing more arguments that
> > can change in size, whereas ** means that args is a dictionary of
> > key=value arguments?
> >[/color]
>
> Why don't you try by yourself in the Python shell ? One of the nice
> things with Python is that it's quite easy to explore and experiment.[/color]

i did try it in a Python shell after i learnt what it was. Like i said
*args will be a list, but when i try **args with the following code it
doesnt work

def test(**args):
keys = args.keys()
for key in keys:
print key+"="+args(ke y)
[color=blue]
>
>
> --
> bruno desthuilliers
> python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
> p in 'onurb@xiludom. gro'.split('@')])"[/color]

[Duncan Booth]

Re: * in Python

placid wrote:
[color=blue]
> i did try it in a Python shell after i learnt what it was. Like i said
> *args will be a list, but when i try **args with the following code it
> doesnt work
>
> def test(**args):
> keys = args.keys()
> for key in keys:
> print key+"="+args(ke y)
>[/color]

When you post here, it helps if instead of saying 'it doesnt work' you say
what you expected to happen and what actually happened (and quote exact
error messages, dont paraphrase them).

If I try your code it works fine: it defines a function.

If I try to call your function, even though you didn't include a call in
what 'doesnt work', then I get the exception I would expect, namely that
you are trying to call args as though it were a function 'args(key)'
instead of subscripting it as a dictionary 'args[key]'. Fixing that will
then generate a different error, but I'm sure you'll be able to figure it
out.

[Bruno Desthuilliers]

Re: * in Python

Duncan Booth wrote:[color=blue]
> Bruno Desthuilliers wrote:
>
>[color=green][color=darkred]
>>>so * basically means that args is a list[/color]
>>
>>A tuple IIRC[/color]
>
>
> In a function definition * means that any remaining position arguments will
> be passed in as a tuple. In a function call the * means that any sequence
> will be unpacked as positional arguments: it doesn't have to be a list or
> a tuple.[/color]

yes, of course - I only saw it from the function's POV.

--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[Bruno Desthuilliers]

Re: * in Python

placid wrote:[color=blue]
> Bruno Desthuilliers wrote:
>[/color]
(snip)[color=blue][color=green]
>>Why don't you try by yourself in the Python shell ? One of the nice
>>things with Python is that it's quite easy to explore and experiment.[/color]
>
>
> i did try it in a Python shell after i learnt what it was. Like i said
> *args will be a list, but when i try **args with the following code it
> doesnt work[/color]

"doesn't work" is the most useless description of a problem.
[color=blue]
> def test(**args):
> keys = args.keys()
> for key in keys:
> print key+"="+args(ke y)[/color]

you want args[key], not args(key)

And you forget to tell how you called this code and what you got.

FWIW:
Python 2.4.3 (#1, Jun 3 2006, 17:26:11)
[GCC 3.4.6 (Gentoo 3.4.6-r1, ssp-3.4.5-1.0, pie-8.7.9)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.[color=blue][color=green][color=darkred]
>>> def test(**kw):[/color][/color][/color]
.... for item in kw.items():
.... print "%s : %s" % item
....[color=blue][color=green][color=darkred]
>>> test()
>>> test(parrot="de ad", walk="silly", nose="big")[/color][/color][/color]
nose : big
parrot : dead
walk : silly[color=blue][color=green][color=darkred]
>>> test(**{'answer ':42})[/color][/color][/color]
answer : 42[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]


--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[placid]

Re: * in Python


Bruno Desthuilliers wrote:[color=blue]
> placid wrote:[color=green]
> > Bruno Desthuilliers wrote:
> >[/color]
> (snip)[color=green][color=darkred]
> >>Why don't you try by yourself in the Python shell ? One of the nice
> >>things with Python is that it's quite easy to explore and experiment.[/color]
> >
> >
> > i did try it in a Python shell after i learnt what it was. Like i said
> > *args will be a list, but when i try **args with the following code it
> > doesnt work[/color]
>
> "doesn't work" is the most useless description of a problem.
>[color=green]
> > def test(**args):
> > keys = args.keys()
> > for key in keys:
> > print key+"="+args(ke y)[/color]
>
> you want args[key], not args(key)
>
> And you forget to tell how you called this code and what you got.[/color]

Too much world cup means sleepless nights down here in Australia or i
would have seen the error with args(key) which suppose to be args[key]
!
[color=blue]
>
> FWIW:
> Python 2.4.3 (#1, Jun 3 2006, 17:26:11)
> [GCC 3.4.6 (Gentoo 3.4.6-r1, ssp-3.4.5-1.0, pie-8.7.9)] on linux2
> Type "help", "copyright" , "credits" or "license" for more information.[color=green][color=darkred]
> >>> def test(**kw):[/color][/color]
> ... for item in kw.items():
> ... print "%s : %s" % item
> ...[color=green][color=darkred]
> >>> test()
> >>> test(parrot="de ad", walk="silly", nose="big")[/color][/color]
> nose : big
> parrot : dead
> walk : silly[color=green][color=darkred]
> >>> test(**{'answer ':42})[/color][/color]
> answer : 42[color=green][color=darkred]
> >>>[/color][/color][/color]

Thanks for that now i know what * means.