On Thu, Jul 26, 2018 at 12:45 PM, David Mertz <me...@gnosis.cx> wrote:
> On Wed, Jul 25, 2018 at 10:29 PM Chris Angelico <ros...@gmail.com> wrote:
>> It is *actually impossible* to
>> perfectly represent short-circuiting semantics in Python!
>
>
> It's INCREDIBLY EASY to represent short-circuiting semantics in Python! What
> on earth are you talking about? That's what the if/elif/else blocks do.
Except for the aforementioned "single lookup, single assignment"
semantics. You can't achieve that with an if/else block.
>> And before you go "well that proves my point, this suggestion is bad",
>> let's
>> apply the same test to a few other pieces of syntax. Rewrite the
>> following statements without using the syntactic feature named in the
>> comment:
>
>
> This is childishly simple:
>
>>
>> # 1) Decorators
>> @deco
>> def func():
>> ...
>
>
> def func():
> ...
> func = deco(func)
Okay. Try this then:
def deco(f):
print(globals()[f.__name__])
return f
func = "funky"
@deco
def func(): pass
Childishly simple? Or does it have its own subtleties? You might think
this is trivial and pointless, but consider the case of a writable
property:
class X:
@property
def spam(self): return 42
@spam.setter
def spam(self, val): print("Setting spam to", val)
This version won't work:
class X:
def spam(self): return 42
spam = property(spam)
def spam(self, val): print("Setting spam to", val)
spam = spam.setter(spam)
See how easy it is to create an imperfect representation?
>> # 3) and the big one: generator expressions
>> # yes, I'm deliberately using x multiple ways here
>> def f(x): return x*x
>> x = range(10)
>> x = (f(x) for x in x if x % 2)
>
>
> I'm not going to bother with that. I'd fire anyone who wrote it, after code
> review. Minus the abuse of names, it's just:
>
> def gen(xs):
>
> for x in xs:
>
> if x % 2:
>
> yield f(x)
>
> x = gen(xs)
Modulo a TON of subtleties about exactly what gets evaluated when.
Again, you've made an imperfect equivalence. So if you're going to
complain about people making ?. equivalences that aren't perfect, make
sure you're just as pedantic about existing syntax. You scored one out
of three, and only by punting to the existing PEP.
ChrisA
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