Should You Be Using Python’s Walrus Operator? (Yes. and Here’s Why) | Hacker News Reader

Should You Be Using Python’s Walrus Operator? (Yes. and Here’s Why)

martinheinz.dev

23 pointsheinzm7 comments

result = [y := func(x), y*2, y*3]

vs.

y = func(x)

result = [y, y*2, y*3]

The latter seems vastly superior to me. Author says > You might say, "I can just add y = func(x) before the list declaration and I don't need the walrus!", you can, but that's one extra, unnecessary line of code and at first glance - without knowing that func(x) is super slow - it might not be clear why the extra y variable needs to exist.

And I think that's stupid

Second example result = [y for x in data if (y := func(x))]

Author says alternative is result = [func(x) for x in data if func(x)]

I say it is

result = [func(x) for x in data]

result = [x for x in result if x] # filter out 0s

While I'm generally of the opinion that walrus shouldn't be used until py3.9's end of life, I'd steelman the second example:

  {x:y
   for x in data
   if (y := f(x))}

Benefit there is that you only iterate over data once (possibly exhasting it) and you only allocate the result list. In 3.9, that takes some wrangling and extra tuple creation/unpacking.

  pairs = ((x,func(x)) for x in data)
  result = {x:y for x,y in pairs if y}

Your criticism sense I to leave out the motivation that the walrus operator in this case leads to an elegant recursion. Edit. Not a recursion, but a reuse of the variable while still getting able to retain a list comprehension.

Well said!

I know we dont get paid by LOC but this recent obsession with compressing everything into a single line is off-putting.

I tend to write code like I used to write assembly.

    x = 5
    y = x + 1
    plot(x, y)

I try to just have each line do one simple thing.

I like the regex example, but the others wouldn't pass code review from me, unfortunately. Reducing a couple lines isn't worth the code being less obvious.

To me it undermines the core appeal of python - simple enough syntax for a beginner to mostly unravel into basic building blocks

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