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Date: Sat, 10 Nov 2012 01:15:36 +1100
Subject: Re: duck typing assert
From: Chris Angelico <rosuav@gmail.com>
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Xref: csiph.com comp.lang.python:33027

On Sat, Nov 10, 2012 at 1:01 AM, Andriy Kornatskyy
<andriy.kornatskyy@live.com> wrote:
>
> 1. In looks-like we check features of Foo (that may be superset) of what IFoo offers.
>
> assert looks(Foo).like(IFoo)
>
> 2. We can check if Foo is limited to IFoo only:
>
> assert looks(IFoo).like(Foo)
>
> So it valid to have both asserts.

You'll almost never need #2, but since there's no difference between a
"class" and an "interface", it's perfectly legal to switch them
around.

But I would generally expect that unrecognized methods are never a
problem (assuming they don't collide with anything) - that, as in
Steven's example, it's fine to have an actor who can sing when you
don't need her to. When you post job openings, you don't normally ask
for someone with "5+ years Python experience and unable to program in
REXX" [1]. You're checking for a minimum set of requirements.

[1] Though I suppose you might ask for someone who's unable to program
in Pascal. Might save you some hassle.

ChrisA