Pythonic way for missing dict keys
aleax at mac.com
Thu Aug 2 17:45:13 CEST 2007
Bruno Desthuilliers <bruno.42.desthuilliers at wtf.websiteburo.oops.com>
> Alex Popescu a écrit :
> > Bruno Desthuilliers <bdesth.quelquechose at free.quelquepart.fr> wrote in
> > news:46b0ed0b$0$2257$426a74cc at news.free.fr:
> >> if hasattr(obj, '__call__'):
> >> # it's a callable
> >> but I don't find it so Pythonic to have to check for a __magic__
> >> method.
> > It looks like Python devs have decided it is Pythonic, because it is
> > already in the PEP.
> I do know, and I disagree with this decision.
> FWIW, repr(obj) is mostly syntactic sugar for obj.__repr__(),
> getattr(obj, name) for obj.__getattr__(name), type(obj) for
> obj.__class__ etc... IOW, we do have a lot of builtin functions that
> mostly encapsulate calls to __magic__ methods, and I definitively don't
> understand why this specific one (=> callable(obj)) should disappear. I
Maybe because it DOESN'T "encapsulate a call" to a magic method, but
rather the mere check for the presence of one?
> usually have lot of respect for Guido's talent as a language designer
> (obviously since Python is still MFL), but I have to say I find this
> particular decision just plain stupid. Sorry.
The mere check of whether an object possesses some important special
method is best accomplished through the abstract-base-classes machinery
(new in Python 3.0: see <http://www.python.org/dev/peps/pep-3119/>). At
this time there is no Callable ABC, but you're welcome to argue for it
on the python-3000 mailing list (please do check the archives and/or
check privately with the PEP owner first to avoid duplication).
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