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Groups > comp.lang.python > #104677

Re: Descriptors vs Property

From Ian Kelly <ian.g.kelly@gmail.com>
Newsgroups comp.lang.python
Subject Re: Descriptors vs Property
Date 2016-03-11 23:37 -0700
Message-ID <mailman.28.1457764672.12893.python-list@python.org> (permalink)
References <nc0b1u$ckq$1@dont-email.me> <mailman.26.1457763193.12893.python-list@python.org> <nc0cgs$fvn$2@dont-email.me>

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On Fri, Mar 11, 2016 at 11:24 PM, Veek. M <vek.m1234@gmail.com> wrote:
> Ian Kelly wrote:
>
>> On Fri, Mar 11, 2016 at 10:59 PM, Veek. M <vek.m1234@gmail.com> wrote:
>>> Also, what's this bit:
>>> self.default = default if default else type()
>>
>> If the default parameter has a truthy value, it gets set to
>> self.default. Otherwise, the type parameter is called with no
>> arguments, and the resulting instance is used as self.default instead.
>
> But type() just gives me:
> TypeError: type() takes 1 or 3 arguments
> on py2,3

You're using the built-in type. In the example, type is the name of
one of the arguments, so its value is whatever was passed in.
Presumably it's meant to be the type that is being checked, and the
result of calling it with no arguments is meant to be a default
instance of that type.

This is not a particularly great example, to be honest. It shadows a
builtin, it makes unwarranted assumptions about the passed-in type,
and the "default if default else type()" expression does not account
for the possibility that the user might actually want to pass in a
default that evaluates as false.

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Thread

Descriptors vs Property "Veek. M" <vek.m1234@gmail.com> - 2016-03-12 11:29 +0530
  Re: Descriptors vs Property Chris Angelico <rosuav@gmail.com> - 2016-03-12 17:05 +1100
  Re: Descriptors vs Property Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-11 23:12 -0700
    Re: Descriptors vs Property "Veek. M" <vek.m1234@gmail.com> - 2016-03-12 11:54 +0530
      Re: Descriptors vs Property Chris Angelico <rosuav@gmail.com> - 2016-03-12 17:35 +1100
      Re: Descriptors vs Property Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-11 23:37 -0700
  Re: Descriptors vs Property "Veek. M" <vek.m1234@gmail.com> - 2016-03-12 11:50 +0530
    Re: Descriptors vs Property Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-12 18:13 +0100
      Re: Descriptors vs Property "Veek. M" <vek.m1234@gmail.com> - 2016-03-13 12:48 +0530
        Re: Descriptors vs Property Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-13 10:25 +0100
          Re: Descriptors vs Property "Veek. M" <vek.m1234@gmail.com> - 2016-03-13 15:26 +0530
            Re: Descriptors vs Property Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-13 11:35 +0100
              Re: Descriptors vs Property "Veek. M" <vek.m1234@gmail.com> - 2016-03-13 18:50 +0530
                Re: Descriptors vs Property Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-13 19:15 +0100
                Re: Descriptors vs Property Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-14 15:34 +0000
                Re: Descriptors vs Property Rustom Mody <rustompmody@gmail.com> - 2016-03-14 10:16 -0700
                Re: Descriptors vs Property Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-16 01:53 +0100
  Re: Descriptors vs Property Ethan Furman <ethan@stoneleaf.us> - 2016-03-16 08:15 -0700

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