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multiple inheritance from list and other class

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  multiple inheritance from list and other class lars van gemerden <lars@rational-it.com> - 2012-01-07 17:16 -0800
    Re: multiple inheritance from list and other class Chris Angelico <rosuav@gmail.com> - 2012-01-08 12:27 +1100
      Re: multiple inheritance from list and other class 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-07 22:08 -0800
      Re: multiple inheritance from list and other class 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-07 22:08 -0800
        Re: multiple inheritance from list and other class Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-08 06:41 +0000
    Re: multiple inheritance from list and other class Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-08 06:42 +0000
      Re: multiple inheritance from list and other class lars van gemerden <lars@rational-it.com> - 2012-01-08 02:48 -0800

#18657 — multiple inheritance from list and other class

Hello,

I have an error message i do not understand:

My code is in essence:

class A(object):
#no __new__ or __init__
    def meth1(self, args):
        #some code
    def meth2(self, args):
        #some code

class B(list, A)
    pass

b = B([1,2,3,4])

error:

Traceback (most recent call last):
  File "D:\Documents\Code\Eclipse\workspace\FlowTools\iteraids.py",
line 431, in <module>
    testolist()
  File "D:\Documents\Code\Eclipse\workspace\FlowTools\iteraids.py",
line 381, in testolist
    b = B([0,1,2,3,4])
TypeError: B() takes exactly 2 arguments (1 given)

(adapted the error to the example classes)

Can anyone help/explain?

Cheers, Lars

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#18658

On Sun, Jan 8, 2012 at 12:16 PM, lars van gemerden <lars@rational-it.com> wrote:
> Hello,
>
> I have an error message i do not understand:
>
> My code is in essence:
>
> b = B([1,2,3,4])
>
> error:
>    b = B([0,1,2,3,4])
> TypeError: B() takes exactly 2 arguments (1 given)

Your code doesn't quite match your error message, and the code as
posted (with 'pass' in the method bodies to make it compile) works
fine. Can you derive a minimal test-case that actually produces the
error in question, and then post the actual code and error? Also -
what version of Python are you using?

Chris Angelico

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#18662

A list is a container. 


Chris Angelico於 2012年1月8日星期日UTC+8上午9時27分06秒寫道：
> On Sun, Jan 8, 2012 at 12:16 PM, lars van gemerden <la...@rational-it.com> wrote:
> > Hello,
> >
> > I have an error message i do not understand:
> >
> > My code is in essence:
> >
> > b = B([1,2,3,4])
> >
> > error:
> >    b = B([0,1,2,3,4])
> > TypeError: B() takes exactly 2 arguments (1 given)
> 
> Your code doesn't quite match your error message, and the code as
> posted (with 'pass' in the method bodies to make it compile) works
> fine. Can you derive a minimal test-case that actually produces the
> error in question, and then post the actual code and error? Also -
> what version of Python are you using?
> 
> Chris Angelico

The class is defined in a silly way. 
In python declaring a class with only trivial properties added is 
not very python at all.

Just let an object obtain new properties to save the troubles of 
deriving a lot classes not different too much.  

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#18663

A list is a container. 


Chris Angelico於 2012年1月8日星期日UTC+8上午9時27分06秒寫道：
> On Sun, Jan 8, 2012 at 12:16 PM, lars van gemerden <la...@rational-it.com> wrote:
> > Hello,
> >
> > I have an error message i do not understand:
> >
> > My code is in essence:
> >
> > b = B([1,2,3,4])
> >
> > error:
> >    b = B([0,1,2,3,4])
> > TypeError: B() takes exactly 2 arguments (1 given)
> 
> Your code doesn't quite match your error message, and the code as
> posted (with 'pass' in the method bodies to make it compile) works
> fine. Can you derive a minimal test-case that actually produces the
> error in question, and then post the actual code and error? Also -
> what version of Python are you using?
> 
> Chris Angelico

The class is defined in a silly way. 
In python declaring a class with only trivial properties added is 
not very python at all.

Just let an object obtain new properties to save the troubles of 
deriving a lot classes not different too much.  

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#18664

On Sat, 07 Jan 2012 22:08:22 -0800, 88888 Dihedral wrote:

[...]
> The class is defined in a silly way.
> In python declaring a class with only trivial properties added is not
> very python at all.

The example given looks like a Mixin class, which is perfectly acceptable 
in Python.



-- 
Steven

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#18665

On Sat, 07 Jan 2012 17:16:22 -0800, lars van gemerden wrote:

> Hello,
> 
> I have an error message i do not understand:
> 
> My code is in essence:

The code you give works fine. It does not show the error you say it does. 
Please test your code before posting and ensure it actually fails the way 
you expect.

It is perfectly fine to use multiple inheritance in the way you show. 
Here is an even simpler example:

py> class Spam(object):
...     pass
... 
py> class Ham(list, Spam):
...     pass
... 
py> 
py> h = Ham([1, 2, 3])
py> 

And no exception is raised.


-- 
Steven

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#18667

On Jan 8, 7:42 am, Steven D'Aprano <steve
+comp.lang.pyt...@pearwood.info> wrote:
> On Sat, 07 Jan 2012 17:16:22 -0800, lars van gemerden wrote:
> > Hello,
>
> > I have an error message i do not understand:
>
> > My code is in essence:
>
> The code you give works fine. It does not show the error you say it does.
> Please test your code before posting and ensure it actually fails the way
> you expect.
>
> It is perfectly fine to use multiple inheritance in the way you show.
> Here is an even simpler example:
>
> py> class Spam(object):
> ...     pass
> ...
> py> class Ham(list, Spam):
> ...     pass
> ...
> py>
> py> h = Ham([1, 2, 3])
> py>
>
> And no exception is raised.
>
> --
> Steven

Sorry for wasting you time, I found the error (had "def" instead of
"class" before B in the example), sorry about not testing, shouldn't
post at 2:00 AM.

Thanks all the same, Lars

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