On Mon, Nov 01, 2021 at 09:39:01AM +0100, Evpok Padding wrote:
> I don't look forward to having to add yet another side note about syntactic
> sugar that does not really add much value (it saves a few characters but
> it's less clear
This proposal is not about saving a few characters. We could keep the
PEP and change the syntax to use a long keyword:
def func(arg=late_binding_through_delayed_evaluation expression)
(where "expression" is an actual expression) and it would still have the
same benefits. Just more awkward to type :-)
> and relying on code to document the parameters is a bit meh
> imo).
Do you think it is a problem that help() can introspect function
signatures and report what the actual defaults are, rather than whatever
lies are put in the docstring? I think that is a fantastic feature for
Python, but it only applies to early defaults.
def func(arg=''):
"""Return a thing.
Arguments: arg is a string, defaults to space.
"""
When possible, the single source of truth for a function's defaults
should be the actual parameter defaults, regardless of when the default
is evaluated.
> Because I won't burden beginners who are already having to ingest a
> lot of thing with a new model of evaluation.
We're not proposing this feature for the benefit of newbies and
beginners. Python is remarkably beginner friendly, but it's not Scratch.
The first edition of Learning Python (Mark Lutz and David Ascher) didn't
introduce function defaults until page 122, right at the end of Chapter
Four. And of course they had to mention the mutable object gotcha. We do
people a disservice if we don't introduce at least the concept of when
the default is evaluated. If we don't, they will invariably trip into
the "mutable default" gotcha on their own and confuse themselves.
I don't think the distinction between early and late binding is a hard
concept to teach. What does this do?
def func(arg=print("Hello")):
return arg
func()
func()
That's all you need to show to demonstrate early binding. Now this:
def func(arg=late print("Hello")):
return arg
func()
func()
Having *both* options available, and teaching it as a choice, will (I
think) make it easier to teach, not harder.
"Write `arg=default` if you want the default to be evaluated just once,
and `arg=late default` if you want the default to be evaluated each time
it is needed. If you are not sure which one you need, use the first."
That's the sort of advice I would have loved when I was a newbie. Short,
simple, straight to the point, and not reliant on knowing what "is None"
means.
--
Steve
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