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Groups > comp.lang.python > #27233

Re: Dynamically determine base classes on instantiation

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On Thursday, 16 August 2012 19:49:43 UTC+2, Steven D'Aprano  wrote:
> On Thu, 16 Aug 2012 10:03:51 -0700, Richard Thomas wrote:
> 
> 
> 
> > class Foo(object):
> 
> >     def __new__(cls, arg):
> 
> >         if isinstance(arg, list):
> 
> >             cls = FooList
> 
> >         elif isinstance(arg, dict):
> 
> >             cls = FooDict
> 
> >         return object.__new__(cls, arg)
> 
> > 
> 
> > class FooList(Foo, list):
> 
> >     pass
> 
> > 
> 
> > class FooDict(Foo, dict):
> 
> >     pass
> 
> 
> 
> 
> 
> Did you actually try your code?
>  

I rarely test code. I'm confident in, however undeserved the confidence. :) In this case that's not an error I've ever seen before. Obvious easy fix:

return cls.__new__(cls, arg)

Incidentally when I reply to your posts through the groups.google.com interface it inserts a blank quoted line between each pair of lines. My first thought was that it was a line endings bug with Google's app but in retrospect that seems very likely to have been fixed years ago. Any ideas?

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Dynamically determine base classes on instantiation Thomas Bach <thbach@students.uni-mainz.de> - 2012-08-15 23:17 +0200
  Re: Dynamically determine base classes on instantiation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 00:16 +0000
    Re: Dynamically determine base classes on instantiation Thomas Bach <thbach@students.uni-mainz.de> - 2012-08-16 14:52 +0200
      Re: Dynamically determine base classes on instantiation Hans Mulder <hansmu@xs4all.nl> - 2012-08-16 17:10 +0200
        Re: Dynamically determine base classes on instantiation Thomas Bach <thbach@students.uni-mainz.de> - 2012-08-16 18:54 +0200
          Re: Dynamically determine base classes on instantiation Richard Thomas <chardster@gmail.com> - 2012-08-16 10:03 -0700
            Re: Dynamically determine base classes on instantiation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 17:49 +0000
              Re: Dynamically determine base classes on instantiation Richard Thomas <chardster@gmail.com> - 2012-08-17 04:50 -0700
                Re: Dynamically determine base classes on instantiation Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-08-17 14:53 -0400
                Re: Dynamically determine base classes on instantiation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-18 01:44 +0000
                Re: Dynamically determine base classes on instantiation Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-18 11:36 +0100
          Re: Dynamically determine base classes on instantiation Richard Thomas <chardster@gmail.com> - 2012-08-16 10:03 -0700
            Re: Dynamically determine base classes on instantiation Thomas Bach <thbach@students.uni-mainz.de> - 2012-08-16 19:27 +0200
      Re: Dynamically determine base classes on instantiation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 18:04 +0000
    Re: Dynamically determine base classes on instantiation Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-08-16 12:29 -0400
    Re: Dynamically determine base classes on instantiation Richard Thomas <chardster@gmail.com> - 2012-08-16 10:09 -0700
      Re: Dynamically determine base classes on instantiation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 17:45 +0000
    Re: Dynamically determine base classes on instantiation Thomas Bach <thbach@students.uni-mainz.de> - 2012-08-16 19:18 +0200
      Re: Dynamically determine base classes on instantiation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 18:08 +0000

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