[Python-ideas] A real life example of "given"

[Neil Girdhar]

On Wed, May 30, 2018 at 1:52 PM Chris Angelico <rosuav at gmail.com> wrote:

> On Thu, May 31, 2018 at 1:23 AM, Peter O'Connor
> <peter.ed.oconnor at gmail.com> wrote:
> >>  In comparison, I think that := is much simpler.
> >
> >
> > In this case that's true, but a small modification:
> >
> >         updates = {
> >             y: do_something_to(potential_update)
> >             for x in need_initialization_nodes
> >             for y in [x, *x.synthetic_inputs()]
> >             if potential_update is not None
> >             given potential_update = command.create_potential_update(y)
> >             }
> >
> > Shows the flexibility of this given syntax vs ":="
>
> I don't understand what you're showcasing here. With :=, you give a
> name to something at the exact point that it happens:
>
>         updates = {
>             y: do_something_to(potential_update)
>             for x in need_initialization_nodes
>             for y in [x, *x.synthetic_inputs()]
>             if (potential_update :=
> command.create_potential_update(y)) is not None
>             }
>
> Personally, I'd use a shorter name for something that's used in such a
> small scope (same as you use one-letter "x" and "y"). But that's the
> only way that the 'given' syntax looks at all better - by encouraging
> you to use yet another line, it conceals some of its immense
> verbosity. (Note how the name "potential_update" is used twice with
> :=, once to set and one to retrieve; but with given, it's used three
> times - retrieve, retrieve, and set.)
>
> How does this show that 'given' is more flexible?
>
>
Oh yeah, good point, I forgot that I could use := within the condition
itself.  It does show that this feature is useful, but not that given is
more flexible than :=.


> ChrisA
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