On Tue, Dec 15, 2020 at 01:16:21PM +0300, Paul Sokolovsky wrote:
> You're now just a step away from the "right answer". Will you make it?
> I did.
Sorry Paul, but you didn't.
You fooled yourself by comparing chalk and cheese, and imagining that
because you can eat cheese (change the order of operation by using
parens, which is a semantic difference), you can also eat chalk (imagine
a semantic difference between `obj.method` and `(obj.method)`).
Your mistake was comparing `(obj.method)()` with `a + (b + c)` when you
should have compared it to `(a + b) + c`. Not every source code
difference has a semantic difference:
x = 1
x=1
x = 1
x = 1 or None
x = (1)
all mean the same thing. Putting parens around the final (1) changes
nothing.
Let's get away from using round brackets for function call, because it
clashes with the use of round brackets for grouping. All we really need
is a *postfix unary operator*.
x() # the brackets are "postfix unary zero-argument function call"
Let's use the factorial operator, "bang" `!` instead.
obj.attr!
has to be evaluated from left to right under Python's rules. You can't
apply the factorial operator until you have looked up attr on obj, and
you cannot lookup attr until you have looked up obj.
So the only possible order of operations is left to right. This is not
meaningful:
# attr factorial first, then lookup obj, then the dot lookup
obj.(attr!)
but while this is meaningful, the order of operations is unchanged:
# lookup obj first, then dot lookup attr, then factorial
(obj.attr)!
Replace the factorial postfix operator with the `()` call operator, and
the logic remains the same.
--
Steve
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