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Why this code works in python3, but not python 2:

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  Why this code works in python3, but not python 2: Maciej Dziardziel <fiedzia@gmail.com> - 2013-07-03 20:52 -0700
    Re: Why this code works in python3, but not python 2: alex23 <wuwei23@gmail.com> - 2013-07-04 14:05 +1000
      Re: Why this code works in python3, but not python 2: Maciej Dziardziel <fiedzia@gmail.com> - 2013-07-03 21:31 -0700
    Re: Why this code works in python3, but not python 2: Chris Angelico <rosuav@gmail.com> - 2013-07-04 14:10 +1000
    Re: Why this code works in python3, but not python 2: Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-04 05:12 +0100
      Re: Why this code works in python3, but not python 2: alex23 <wuwei23@gmail.com> - 2013-07-04 14:47 +1000
        Re: Why this code works in python3, but not python 2: Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-04 06:10 +0100

#49802 — Why this code works in python3, but not python 2:

Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:

def foo(*args, bar=1, **kwargs):
    pass


-- 
Maciej Dziardziel

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#49803

On 4/07/2013 1:52 PM, Maciej Dziardziel wrote:
> Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:
>
> def foo(*args, bar=1, **kwargs):
>      pass

It was an explicit syntax change for Python3. You can read about the
reasoning behind it here:

http://www.python.org/dev/peps/pep-3102/

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#49808

On Thursday, July 4, 2013 5:05:23 AM UTC+1, alex23 wrote:
> It was an explicit syntax change for Python3. You can read about the
> reasoning behind it here:
> 
> http://www.python.org/dev/peps/pep-3102/

Thanks, that was helpful.

Maciej Dziardziel

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#49805

On Thu, Jul 4, 2013 at 1:52 PM, Maciej Dziardziel <fiedzia@gmail.com> wrote:
> Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:
>
> def foo(*args, bar=1, **kwargs):
>     pass

Keyword-only arguments are (IIRC) a Py3-only feature. There are lots
of features that don't work in Python 2 - that's simply the way things
happen with old versions of software.

ChrisA

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#49806

On 4 July 2013 04:52, Maciej Dziardziel <fiedzia@gmail.com> wrote:
> Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:
>
> def foo(*args, bar=1, **kwargs):
>     pass

Python 3 gained syntax for keyword-only arguments.

Try "foo(1)" and it will fail -- "bar" needs to be given as a keyword.
This is because it comes after a *-expression. You can also do "def
foo(*, bar=1)" if you want bar to be keyword-only without accepting
any number of positional arguments. Python 2 does not have these, and
doesn't understand the syntax for them.

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#49810

On 4/07/2013 2:12 PM, Joshua Landau wrote:
> On 4 July 2013 04:52, Maciej Dziardziel <fiedzia@gmail.com> wrote:
>> def foo(*args, bar=1, **kwargs):
>>      pass

> Try "foo(1)" and it will fail -- "bar" needs to be given as a keyword.

No it won't, because it is supplied with a default. You may be
confusing it with the requirement that `bar` must be given as a keyword
in order for it to override the default, compared to the way this would
need to be written in Py2:

     def foo(bar=1, *args, **kwargs):
         ...

...in which case `bar` could be assigned to by the first positional
argument.

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#49812

On 4 July 2013 05:47, alex23 <wuwei23@gmail.com> wrote:
> On 4/07/2013 2:12 PM, Joshua Landau wrote:
>>
>> On 4 July 2013 04:52, Maciej Dziardziel <fiedzia@gmail.com> wrote:
>>>
>>> def foo(*args, bar=1, **kwargs):
>>>      pass
>
>
>> Try "foo(1)" and it will fail -- "bar" needs to be given as a keyword.
>
>
> No it won't, because it is supplied with a default.

Pah! I'm not even thinking.

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