On 2021-10-30 18:29, Chris Angelico wrote:
> What I am saying is that there is a qualitative difference between "I
>know now (at function definition time) what value to use for this
>argument if it's missing" and "I know now (at function definition time)
>*what I will do* if this argument is missing". Specifying "what you
>will do" is naturally what you do inside the function. It's a process
>to be done later, it's logic, it's code. It is not the same as
>finalizing an actual VALUE at function definition time. So yes, there
>is a qualitative difference between:
>
># this
>if argument is undefined:
> argument = some_constant_value
>
># and this
>if argument is undefined:
> # arbitrary code here
>
> I mean, the difference is that in one case arbitrary code is allowed!
>That's a big difference.
Right. That is a very real difference, which is why there is a very
real difference between early-bound and late-bound defaults. But both
are argument defaults.
I don't 100% agree with that.
I mean, here's another way to come at this. Suppose we have this under
the proposal (using some random syntax picked at random):
def foo(a=1, b="two", c@=len(b), d@=a+c):
You keep saying that c and d "are argument default" just like a and b.
So can you tell me what the argument default for each of those arguments?
The default for argument a is an integer. The default for argument b
is a string. Can you tell me, in comparable terms, what the defaults
for arguments c and d are?
Currently, every argument default is a first-class value. As I
understand it, your proposal breaks that assumption, and now argument
defaults can be some kind of "construct" that is not a first class
value, not any kind of object, just some sort of internal entity that no
one can see or manipulate in any way, it just gets automatically
evaluated later.
I really don't like that. One of the things I like about Python is the
"everything is an object" approach under which most of the things that
programmers work with, apart from a very few base syntactic constructs,
are objects. Many previous expansions to the language, like decorators,
context managers, the iteration protocol, etc., worked by building on
this object model. But this proposal seems to diverge quite markedly
from that.
If the "late-bound default" is not an object of some kind just like the
early-bound ones are, then I can't agree that both "are argument defaults".
--
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is no
path, and leave a trail."
--author unknown
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