stephanh42 at gmail.com
Fri May 19 14:32:44 EDT 2017
Let me quote the attrs docs:
convert (callable) – callable() that is called by attrs-generated __init__
methods to convert attribute’s value to the desired format. It is given the
passed-in value, and the returned value will be used as the new value of
the attribute. The value is converted before being passed to the validator,
So the signature is essentially:
self.myattrib = callable (myattrib)
Op 19 mei 2017 20:25 schreef "Guido van Rossum" <guido at python.org>:
> For people who don't want to click on links:
> 1. Allow hash and equality to be based on object identity, rather than
> structural identity,
> this is very important if one wants to store un-hashable objects in
> the instance.
> (In my case: mostly dict's and numpy arrays).
> 2. Not subclassed from tuple. I have been bitten by this subclassing
> when trying to set up
> singledispatch on sequences and also on my classes.
> 3. Easily allow to specify default values. With namedtuple this
> requires overriding __new__.
> 4. Easily allow to specify a conversion function. For example I have
> some code like below:
> note that I can store a numpy array while keeping hashability and
> I can make it convert
> to a numpy array in the constructor.
> @attr.s(cmp=False, hash=False)
> class SvgTransform(SvgPicture):
> child = attr.ib()
> matrix = attr.ib(convert=numpy.asarray)
> I have one question about (4) -- how and when is the conversion function used, and what is its signature?
> On Fri, May 19, 2017 at 5:42 AM, Eric V. Smith <eric at trueblade.com> wrote:
>> Could you point me to this 4-point list of Stephan's? I couldn't find
>>> anything in the archive that you might be referring to.
>> Never mind, I found them here:
>> Python-ideas mailing list
>> Python-ideas at python.org
>> Code of Conduct: http://python.org/psf/codeofconduct/
> --Guido van Rossum (python.org/~guido)
> Python-ideas mailing list
> Python-ideas at python.org
> Code of Conduct: http://python.org/psf/codeofconduct/
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