On 02/12/2021 03:35, Steven D'Aprano wrote:
On Wed, Dec 01, 2021 at 05:16:34PM +1100, Chris Angelico wrote:
1) If this feature existed in Python 3.11 exactly as described, would
you use it?
Yes I would, but probably not as often as counting cases of the "if
param is None: ..." idiom might lead you to expect.
The problem is, as Neil also pointed out, that it becomes tricky to
explicitly ask for the default behaviour except by leaving the argument
out altogether. Not impossible, as Chris mentions elsewhere, you can
mess about with `*args` or `**kwargs`, but it is decidedly less
convenient, more verbose, and likely to have a performance hit.
So if I were messing about in the interactive interpreter, I would
totally use this for the convenience:
def func(L=>[]): ...
but if I were writing a library, I reckon that probably at least half
the time I'll stick to the old idiom so I can document the parameter:
"If param is missing **or None**, the default if blah..."
I reject Chris' characterisation of this as a hack. There are function
parameters where None will *never* in any conceivable circumstances
become a valid argument value, and it is safe to use it as a sentinel.
There are also circumstances when you start off thinking that None will
never be a valid argument value, but later you have to cater for it.
Now it does start to look as if you used a hack.
Best wishes
Rob Cliffe
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