Why python doesn't use syntax like function(, , x) for default parameters?
steve at REMOVETHIScyber.com.au
Sat Mar 11 01:48:56 CET 2006
On Fri, 10 Mar 2006 12:06:57 +0300, 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'm confused... it looks to me like the defaults are *first*, not last, in
the above definition. We write from left to write in English, so normal
convention in English is that first -> last, not last <- first.
> and when calling, just omit parameter when you want to
> use defaults:
> a_func(, , 3)
Can you do this? another_func(,,,4,,,,)
That looks like bug-city to me. (Did I mean 4 to go in the fourth position
In any case, given the way Python defaults work, the commas are
superfluous. There is no ambiguity:
def f(w, x, y=1, z=1):
Positional arguments without defaults *must* go first, and must be
f(5, 6) => w=5, x=6, y=1, z=1
Commas would be pointless: f(5, 6, , ) isn't needed, because the first
and second arguments are already assigned to the w and x arguments before
the first empty comma is spotted.
You can't do this: f(, , 5, 6) => w,x = default, y=5, z=6
because w and x don't have defaults.
> 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.
And you think it is easier to remember the position of parameters rather
than their names?
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