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From: Andriy Kornatskyy <andriy.kornatskyy@live.com>
To: <rosuav@gmail.com>, "python-list@python.org" <python-list@python.org>
Subject: RE: duck typing assert
Date: Fri, 9 Nov 2012 13:26:36 +0300
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Xref: csiph.com comp.lang.python:33008


Thank you for all comments.

> It=A0makes very good sense to say:
>
> duckmatch(IFoo).compare(Foo)

Since we do duck match of IFoo... but there is no `duck match`=2C there is =
`duck test`.=A0I believe instead of `compare` is more readable with `equals=
`. Than it is more from=A0mathematics - precise answer...=A0that you can no=
t guarantee at all in dynamic programming language. So it false to use such=
 wording to reflect this check. We can only make an assumption that one loo=
ks like the other (similar)... with some limitation of cause... understandi=
ng what is `duck test`.

http://en.wikipedia.org/wiki/Duck_test

The intent is to make such language `construct` so it reads as English sent=
ence that make sense=2C and not mandatory `pythonic` way (readability count=
s=2C java smokes aside).

is_similar(Foo).to(IFoo) # <=3D but we lost `duck test` sense here?

Words `looks` and `like` are coming from duck test and point also direction=
:

# 1
looks(Foo).like(IFoo=2C notice=3D['__len__']=2C ignore_funcs=3D['foo']=2C i=
gnore_argspec['bar'])

English sentence equivalent: if functions in Foo looks like one in IFoo tha=
n=2C probably=2C IFoo can be replaced with Foo=3B notice to check __len__=
=2C it is safe to ignore function `foo` and arguments passed to `bar`.

# 2
looks(Foo=2C notice=3D['__len__']=2C ignore_funcs=3D['foo']=2C ignore_argsp=
ec['bar']).like(IFoo)

English sentence equivalent:=A0while looking at Foo notice to check `__len_=
_`=2C it is safe to ignore function `foo` and=A0arguments passed to `bar`=
=2C than probably it like IFoo.

I think #1 is easier to understand once it is written. Thoughts?

Also construction=A0looks(Foo).like(IFoo) points direction of check. It you=
 need the two be replaceable you need two asserts:

assert looks(Foo).like(IFoo)
assert looks(IFoo).like(Foo)

Thanks.

Andriy Kornatskyy


----------------------------------------
> Date: Fri=2C 9 Nov 2012 17:14:49 +1100
> Subject: Re: duck typing assert
> From: rosuav@gmail.com
> To: python-list@python.org
>
> On Fri=2C Nov 9=2C 2012 at 12:00 PM=2C Ian Kelly <ian.g.kelly@gmail.com> =
wrote:
> > looks(Foo).like(IFoo)=2C on the other hand=2C is crystal clear about wh=
ich
> > argument is which.
>
> I'm not so sure that it is=2C tbh. If you read it like an English
> sentence=2C it's clearly testing whether Foo matches the template in
> IFoo=2C but which are you more likely to do: test one class to see if it
> satisfies lots of templates=2C or test one template against every class
> you meet? I think probably the latter is=2C if not more likely than the
> former=2C at least sufficiently plausible as to create confusion. It
> makes very good sense to say:
>
> duckmatch(IFoo).compare(Foo)
>
> ie with the arguments the other way.
>
> ChrisA
> --
> http://mail.python.org/mailman/listinfo/python-list
 		 	   		  =