Why python doesn't use syntax like function(, , x) for default parameters?

Steve Holden steve at holdenweb.com
Fri Mar 10 14:17:24 CET 2006


Dmitry Anikin wrote:
> I mean, it's very convenient when default parameters
> can be in any position, like
> def a_func(x = 2, y = 1, z):
>     ...
> (that defaults must go last is really a C++ quirk which
> is needed for overload resolution, isn't it?)
> 
I've no idea why C++ required defaults last; it certainly seems wise to 
avoid confusion with the positionals in Python.

> and when calling, just omit parameter when you want to
> use defaults:
> a_func(, , 3)
> 
Yerch! So now you've forced all arguments to be positional? This doesn't 
seem like an improvement. And it's just plain fugly.

> There are often situations when a function has independent
> parameters, all having reasonable defaults, and I want to
> provide just several of them. In fact, I can do it using
> keyword parameters, but it's rather long and you have to
> remember/lookup names of parameters.
> 
Whereas you can invariably remember their positions? I don't think so.

> Is there some contradiction in python syntax which disallows
> an easy implementation of this feature, or just nobody bothered
> with this? If former is the case, please show me why, because
> I badly need this feature in embedded python app (for
> compatibility with other language that uses such syntax) and might
> venture to implement it myself, so don't want to waste time
> if it's gonna break something.
> Or maybe it might be an idea for enhancement proposal?
> 
The thing about enhancement proposals is that they are supposed to 
*improve* the language. Frankly I wouldn't see this as any kind of 
enhancement.

If you have a large program to translate from another language you will 
probably find that a modest application of Python suffices to translate 
all the calls into whatever form turns out to be required in Python.

regards
  Steve
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
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