[Python-Dev] (name := expression) doesn't fit the narrative of PEP 20 (original) (raw)

Ethan Furman ethan at stoneleaf.us
Wed Apr 25 18:15:53 EDT 2018

On 04/25/2018 02:55 PM, Tim Peters wrote:

This becomes a question of seasoned judgment. For example, here's a real loop summing a series expansion, until the new terms become so small they make no difference to the running total (a common enough pattern in code slinging floats or decimals):

while True: old = total total += term if old == total: return total term = mx2 / (i(i+1)) i += 2 To my eyes, this is genuinely harder to follow, despite its relative brevity: while total != (total := total + term): term = mx2 / (i(i+1)) i += 2 return total So I wouldn't use binding expressions in that case. I don't have a compelling head argument for why I find the latter spelling harder to follow, but I don't need a theory to know that I in fact do.

I know why I do: I see "while total != total" and my gears start stripping. On the other hand,

while total != (total + term as total): ...

I find still intelligible. (Yes, I know "as" is dead, just wanted to throw that out there.)

-- Ethan

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