[Python-ideas] PEP 572: Assignment Expressions (post #4)

[Brendan Barnwell]

On 2018-04-11 05:23, Clint Hepner wrote:
> I find the assignments make it difficult to pick out what the final expression looks like.

	I strongly agree with this, and for me I think this is enough to push 
me to -1 on the whole proposal.  For me the classic example case is 
still the quadratic formula type of thing:

x1, x2 = (-b + sqrt(b**2 - 4*a*c))/2, (-b - sqrt(b**2 - 4*a*c))/2

	It just doesn't seem worth it to me to create an expression-level 
assignment unless it can make things like this not just less verbose but 
at the same time more readable.  I don't consider this more readable:

x1, x2 = (-b + sqrt(D := b**2 - 4*a*c)))/2, (-b - sqrt(D))/2

. . . because having to put the assignment inline creates a visual 
asymmetry, when for me the entire goal of an expression-level statement 
is to make the symmetry between such things MORE obvious.  I want to be 
able to write:

x1, x2 = (-b + sqrt(D)))/2, (-b - sqrt(D))/2 ...

. . . where "..." stands for "the part of the expression where I define 
the variables I'm re-using in multiple places in the expression".

	The new proposal does at least have the advantage that it would help 
with things like this:

while x := some_function_call():
	# do stuff

	So maybe I'm -0.5 rather than -1.  But it's not just that this proposal 
"could be used to create ugly code".  It's that using it for 
expression-internal assignments WILL create ugly code, and there's no 
way to avoid it.  I just don't see how this proposal provides any way to 
make things like the quadratic formula example above MORE readable.

-- 
Brendan Barnwell
"Do not follow where the path may lead.  Go, instead, where there is no 
path, and leave a trail."
    --author unknown