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Re: Differences creating tuples and collections.namedtuples

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From Gregory Ewing <greg.ewing@canterbury.ac.nz>
Newsgroups comp.lang.python
Subject Re: Differences creating tuples and collections.namedtuples
Date Tue, 19 Feb 2013 20:54:49 +1300
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Steven D'Aprano wrote:

> Terry Reedy wrote:

>>In fact, one reason to subclass a class is to change the initialization
>>api.

> That might be a reason that people give, but it's a bad reason from the
> perspective of interface contracts, duck-typing and the LSP.

Only if you're going to pass the class off to something as
a factory function.

Note that having a different constructor signature is *not*
an LSP violation for *instances* of a class. The constructor
is not part of the interface for instances, only for the
class itself.

In practice, it's very common for a class to have a different
constructor signature from its base class, and this rarely
causes any problem.

IPython is simply making a dodgy assumption. It gets away with
it only because it's very rare to encounter subclasses of
list or tuple at all.

-- 
Greg

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Differences creating tuples and collections.namedtuples John Reid <johnbaronreid@gmail.com> - 2013-02-18 03:47 -0800
  Re: Differences creating tuples and collections.namedtuples Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-18 12:03 +0000
  Re: Differences creating tuples and collections.namedtuples Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-18 12:05 +0000
  Re: Differences creating tuples and collections.namedtuples Dave Angel <davea@davea.name> - 2013-02-18 07:11 -0500
  Re: Differences creating tuples and collections.namedtuples John Reid <johnbaronreid@gmail.com> - 2013-02-18 13:49 +0000
  Re: Differences creating tuples and collections.namedtuples John Reid <johnbaronreid@gmail.com> - 2013-02-18 13:51 +0000
  Re: Differences creating tuples and collections.namedtuples John Reid <j.reid@mail.cryst.bbk.ac.uk> - 2013-02-18 14:09 +0000
    Re: Differences creating tuples and collections.namedtuples raymond.hettinger@gmail.com - 2013-02-18 23:48 -0800
      Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-19 08:06 +0000
      Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-19 08:57 +0000
      Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-19 08:06 +0000
      Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-19 08:05 +0000
    Re: Differences creating tuples and collections.namedtuples raymond.hettinger@gmail.com - 2013-02-18 23:48 -0800
  Re: Differences creating tuples and collections.namedtuples Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-18 14:15 +0000
  Re: Differences creating tuples and collections.namedtuples John Reid <johnbaronreid@gmail.com> - 2013-02-18 14:18 +0000
  Re: Differences creating tuples and collections.namedtuples Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-18 14:12 +0000
  Re: Differences creating tuples and collections.namedtuples John Reid <j.reid@mail.cryst.bbk.ac.uk> - 2013-02-18 14:23 +0000
  Re: Differences creating tuples and collections.namedtuples Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-18 14:53 +0000
  Re: Differences creating tuples and collections.namedtuples John Reid <j.reid@mail.cryst.bbk.ac.uk> - 2013-02-18 15:07 +0000
  Re: Differences creating tuples and collections.namedtuples Terry Reedy <tjreedy@udel.edu> - 2013-02-18 16:28 -0500
    Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-19 11:18 +1100
      Re: Differences creating tuples and collections.namedtuples Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-19 01:43 +0000
        Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-19 14:06 +1100
          Re: Differences creating tuples and collections.namedtuples Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-02-19 21:27 +1300
      Re: Differences creating tuples and collections.namedtuples Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-02-19 20:54 +1300
      Re: Differences creating tuples and collections.namedtuples John Reid <j.reid@mail.cryst.bbk.ac.uk> - 2013-02-19 09:30 +0000
      Re: Differences creating tuples and collections.namedtuples Terry Reedy <tjreedy@udel.edu> - 2013-02-19 22:38 -0500
        Re: Differences creating tuples and collections.namedtuples Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-22 10:38 +0000
      Re: Differences creating tuples and collections.namedtuples Chris Angelico <rosuav@gmail.com> - 2013-02-20 17:50 +1100
        Re: Differences creating tuples and collections.namedtuples Roy Smith <roy@panix.com> - 2013-02-20 09:09 -0500
    Re: Differences creating tuples and collections.namedtuples Roy Smith <roy@panix.com> - 2013-02-18 20:11 -0500
  Re: Differences creating tuples and collections.namedtuples alex23 <wuwei23@gmail.com> - 2013-02-18 17:47 -0800
    Re: Differences creating tuples and collections.namedtuples John Reid <j.reid@mail.cryst.bbk.ac.uk> - 2013-02-19 09:36 +0000

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