On 1 Jun 2016, at 17:59, Steven D'Aprano email@example.com wrote:
On Tue, May 31, 2016 at 10:35:01AM -0700, David Mertz wrote:
For things like namedtuple that need more arguments, you'd need to use functools.partial to create the single argument callable to match the syntax.
As far as I am concerned, limiting it to single-argument functions cripples this proposal to the point that it is of no interest.
So far I've seen exactly four real-world use-cases, plus potentially Django. Only supporting a single name makes this useless for two of those use-cases, and I predict all of the Django examples. Using partial is *more work than the status quo* which means nobody in their right mind is going to use it.
# (1) status quo Record = namedtuple("Record", fields)
# (2a) my suggestion Record -> namedtuple(fields)
# (2b) or if you insist def Record = namedtuple(fields)
# (3) if it only supports a single argument from functools import partial Record -> partial(namedtuple, field_names=fields)()
That is significantly more annoying than the status quo. But it gets worse! Remember that partial() binds positional arguments from the left, which is the wrong side for what we need. Fortunately namedtuple supports keyword arguments, but what about those that don't?
For the sake of the exercise, let's pretend that namedtuple doesn't support keyword arguments, just to get an idea of how to solve it:
Record -> partial(lambda fields, name: namedtuple(name, fields), fields)()
And let's just hope nobody wants to call namedtuple with the other arguments, verbose or rename.
It is easy to wave your hands and say "just use partial", but not so easy to *actually do so*.
I'm working under the assumption that "eventually" the functions get reworked so as to return a 1-argument function.
So (using the -> syntax)
x -> Symbol Point -> namedtuple_wrapper(['x', 'y'])
x = Symbol('x') Point = namedtuple_wrapper(['x', 'y'])('Point')
Adding the name as a first argument looks even more hacky to me, to be honest.
x, y, z -> expr
Should raise a syntax-error for all I care. Unless everybody agrees that it should call the naming creator 3 times? I would find it confusing, to be honest.
So it would be
identifier -> expression
identifier_list -> expression