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Re: Chanelling Guido - dict subclasses

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Date Wed, 15 Jan 2014 05:03:25 -0600
From Tim Chase <python.list@tim.thechases.com>
To python-list@python.org
Subject Re: Chanelling Guido - dict subclasses
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Xref csiph.com comp.lang.python:63969

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On 2014-01-15 01:27, Steven D'Aprano wrote:
> class TextOnlyDict(dict):
>     def __setitem__(self, key, value):
>         if not isinstance(key, str):
>             raise TypeError
>         super().__setitem__(key, value)
>     # need to override more methods too
> 
> 
> But reading Guido, I think he's saying that wouldn't be a good
> idea. I don't get it -- it's not a violation of the Liskov
> Substitution Principle, because it's more restrictive, not less.
> What am I missing?

Just as an observation, this seems almost exactly what anydbm does,
behaving like a dict (whether it inherits from dict, or just
duck-types like a dict), but with the limitation that keys/values need
to be strings.

-tkc

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Thread

Chanelling Guido - dict subclasses Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-01-15 01:27 +0000
  Re: Chanelling Guido - dict subclasses Ned Batchelder <ned@nedbatchelder.com> - 2014-01-14 21:04 -0500
  Re: Chanelling Guido - dict subclasses Terry Reedy <tjreedy@udel.edu> - 2014-01-14 22:48 -0500
  Re: Chanelling Guido - dict subclasses F <f@hop2it.be> - 2014-01-15 07:00 +0000
  Re: Chanelling Guido - dict subclasses Peter Otten <__peter__@web.de> - 2014-01-15 09:40 +0100
    Re: Chanelling Guido - dict subclasses John Ladasky <john_ladasky@sbcglobal.net> - 2014-01-15 08:51 -0800
      Re: Chanelling Guido - dict subclasses Peter Otten <__peter__@web.de> - 2014-01-15 19:35 +0100
      Re: Chanelling Guido - dict subclasses Devin Jeanpierre <jeanpierreda@gmail.com> - 2014-01-15 22:30 -0800
  Re: Chanelling Guido - dict subclasses Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-15 09:10 +0000
  Re: Chanelling Guido - dict subclasses Tim Chase <python.list@tim.thechases.com> - 2014-01-15 05:03 -0600
  Re: Chanelling Guido - dict subclasses Daniel da Silva <var.mail.daniel@gmail.com> - 2014-01-15 19:50 -0500
    Re: Chanelling Guido - dict subclasses Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-01-16 17:17 +1300

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