On May 11, 2018 1:45:27 PM Tim Peters <tim.pet...@gmail.com> wrote:
[Brendan Barnwell]
. . . and it's true the latter is a bit more verbose in that case for
little extra benefit. But when the locally-defined value is used within
a more complicated expression (like the quadratic formula example), I
think readability goes down significantly. To appease Tim, instead of
using the quadratic formula, though, I will use a more realistic example
that comes up fairly often for me: wanting to do some kind of
normalization on a piece of data for a comparison, while keeping the
unnormalized data for use within the block:
if some_condition and (stuff:=
get_user_input()).lower().strip().replace('-', ''):
versus
if some_condition and stuff.lower().strip().replace('-', '') given
stuff = get_user_input():
[also Brendan]
Ironically I weakened my argument by forgetting to finish my
expression there. I intended that chain of method calls to be used in a
comparison to make the surrounding expression more complex. So revise the
above to
if some_condition and (stuff :=
get_user_input()).lower().strip().replace('-', '') == existing_value:
versus
if some_condition and stuff.lower().strip().replace('-', '') ==
existing_value given stuff = get_user_input():
Even more ironically, to my eyes the original more strongly supported
your view than the rewrite ;-)
"given stuff =" stuck out in the original because it was preceded by
punctuation (a right parenthesis).
I had to read the rewrite 3 times before i realized you were even
_using_ "given", because there it's buried between two other names -
"existing_value given stuff" - and visually looks more like it's
actually the 3rd of 4 words (because of the underscore in
"existing_value").
There are some variants of tanks like 'if let' where the bindings come
*first*, unlike 'given' where they come last (like Haskell's 'where').
Of course that would have been obvious in a Python-aware editor that
colored "given" differently, but as-is I found the original easy to
read but the rewrite a puzzle to decode.
Well, you've partly explained the reason: our eyes are drawn to what sticks
out. In this case, the := stuck out in a section heavy on black letters. In
a proper editor, it may even be the other way around: they tend to
highlight keywords in a stronger manner (like bolding) than operators.
Similarly, in the rewritten assignment expression spelling, it's
obvious at a glance that the test is of the form
some_condition and some_messy_expression == existing_value
but in the rewritten "given" sample that's obscured because
"existing_value" not only doesn't end the statement, it's not even
followed by punctuation. Of course coloring "given" differently would
remove that visual uncertainty too. For a dumb display, I'd write it
if some_condition and (
stuff.lower().strip().replace('-', '') == existing_value) given
stuff = get_user_input():
instead (added parens so that "existing_value" and "given" are
separated by punctuation).
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