On Sat, Aug 29, 2020, 2:24 PM Paul Moore <p.f.mo...@gmail.com> wrote:
> On Sat, 29 Aug 2020 at 18:04, Jonathan Fine <jfine2...@gmail.com> wrote:
> >
> > Paul Moore wrote:
> >
> >> But you don't give any reason why you'd want to do that. Why are you
> >> using subscript notation rather than a simple function call?
> >
> >
> > Good point. Consider
> > >>> def f(*argv): pass
> > >>> d = dict()
> >
> > Now compare
> > >>> f(1, 2) = 3
> > SyntaxError: can't assign to function call
> > >>> d[1, 2] = 3
> > >>> d[1, 2]
> > 3
>
> Obviously. As it says, you can't assign to a function call.
>
> > Item assignment (ie __setitem__) is the one thing that a function call
> can't do. If we want keywords in our __getitem__ and so on commands, then
> one route for item assignment is to allow
> > >>> d[1, 2, a=3, b=4] = 5
> > as valid syntax.
>
> Again, obvious. But you still haven't given any reason why we would
> want to do that. No-one's arguing that these things aren't possible,
> or that the proposals can't be implemented. What I'm asking, and you
> aren't answering, is what is the use case? When, in real world code,
> would this be used?
>
I'd like to use syntax like this for defining a named mathematical
functions:
>>> f, g, h = mymath.funcs("f g h")
>>> x, y, z = mymath.vars("x y z")
>>> f[x] = x**2 + 2*x + 1
>>> g[x, y] = x**2 + x*y + y**2
>>> h[z] = f[z] + g[1, z]
>>> h[2]
15
>>> h[z=2]
15
Why? Because it looks like handwritten math. Far more pleasant for my
colleagues to read than lambda expressions and def statements.
I can already do most of this now of course (on fact, I have). But it'll be
far far easier to write, read, and maintain the supporting code with
function-like argument parsing in subscripts.
>
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