duck typing assert

Chris Angelico rosuav at
Fri Nov 9 15:15:36 CET 2012

On Sat, Nov 10, 2012 at 1:01 AM, Andriy Kornatskyy
<andriy.kornatskyy at> 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

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.


More information about the Python-list mailing list