On Thu, May 31, 2018 at 04:06:51AM +1000, Chris Angelico wrote:
> On Thu, May 31, 2018 at 3:59 AM, Neil Girdhar <mistersheik@gmail.com> wrote:
> > This example shows additional flexibility:
> >
> > z = {a: transformed_b
> > for b in bs
> > given transformed_b = transform(b)
> > for a in as_}
> >
> > There is no nice, equivalent := version as far as I can tell.
>
> True. However, it took me several readings to understand what you were
> doing here.
Possibly you shouldn't have tried reading at 4am.
Either that or I shouldn't be reading before I've had a coffee :-)
Have I missed something that you have seen? Even if the syntax were
legal, that seems to be a pointless use of an assignment expression.
Since the new name "transformed_b" is only used once, we can and should
just use the transform(b) in place:
z = {a: transform(b) for b in bs for a in as_}
Chris just explained it to you. You're calling transform too often.
If we need to use it twice, we can do this:
# assume "@" stands in for something useful
z = {a: (transformed_b := transform(b)) @ transformed_b
for b in bs for a in as_}
I'm not seeing the advantage of given, or any extra flexibility here,
unless the aim is to encourage people to make syntax errors :-)
The flexibility of "given" is in giving names to elements of expressions and comprehensions to avoid recalculation.
What have I missed?
Like you say, := and given both work for expressions. "given" could theoretically also be used in comprehensions.
--
Steve
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