On Tue, 23 Feb 2021 at 09:25, Steven D'Aprano <st...@pearwood.info> wrote:
>
> On Mon, Feb 15, 2021 at 09:29:45AM -0800, Guido van Rossum wrote:
>
> > Proposals like this always baffle me. Python already has both anonymous and
> > named functions. They are spelled with 'lambda' and 'def', respectively.
> > What good would it do us to create an alternate spelling for 'def'?
> [...]
>
>
> I think that the desire probably comes from thinking of short
> mathematical functions where the body is a simple expression, like in
> maths:
[...]
> So there is definitely some aesthetic advantage to the arrow if you're
> used to maths notation, and if Python had it, I'd use it.
Yes, this is precisely my instinct as well.
In addition, for whatever reason (and it's purely subjective, I won't
try to defend it) I find "lambda" as a keyword somewhat alien in
Python, where most other keywords are short terms or abbreviations of
terms (and the terms are mostly non-technical English words - "with",
"for", "def(ine)", "class", ...). So every time I use a lambda
expression, it feels mildly unnatural to me, and I look for a "better
way" of expressing my intent. But having a mathematical background,
functional and comprehension styles feel natural to me, which
introduces a tension - so, for example, I recently wrote some code
that included the following:
squares = set(takewhile(lambda sq: sq <= 2 * end, map(lambda x: x
* x, count())))
A procedural version would be
squares = set()
x = 1
while True:
sq = x * x
if sq > 2 * end: break
squares.add(sq)
x += 1
and a *lot* of people would say this is easier to read, but IMO, both
should have a comment explaining what "squares" is, and the
itertools-based version took me less time to write, and ensure I'd got
correct.
I'd find a version using "arrow notation"
squares = set(takewhile(sq => (sq <= 2 * end), map(x => x * x, count())))
easier to read than the lambda version (personally I prefer => over
->, but that's a detail) even though I needed to add parentheses to
(sq <= 2 * end) to make it clear what was the expression and what was
the argument.
Honestly, none of these scream to me "the set of squares less than end
* 2", though, so it's difficult to say any one of them is the
"obvious" choice. But I'd probably order them as =>, lambda,
procedural (from best to worst). This is when writing that code in a
Jupyter notebook as part of some exploratory work. If this were
production-level code where others would be maintaining it, I'd write
a standalone function that wrapped the procedural code, give it a name
and a docstring, and add some tests to it. But not all code is like
that (not even all "important" code) so sometimes the one-liners make
sense.
> But it doesn't scale up to multi-statement functions, and doesn't bring
> any new functionality into the language, so I'm not convinced that
> its worth adding as a mere synonym for def or lambda or both.
Yep, it's a difficult call. I suspect that if Python had been
developed now, it would have followed the trend of using arrow
notation. But adding it as a synonym for the existing lambda is
nowhere near as obvious a choice.
Paul
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