[Python-Dev] Examples for PEP 572 (original) (raw)

Steven D'Aprano steve at pearwood.info
Wed Jul 4 14:21:46 EDT 2018

On Wed, Jul 04, 2018 at 08:33:17PM +0300, Ivan Pozdeev via Python-Dev wrote:

>>while total != (total := total + term): >> term = mx2 / (i(i+1)) >> i += 2 >>return total

[...]

It took me a few minutes to figure out that this construct actually checks term == 0.

That's badly wrong.

Hint: it's floating point code. total and term are floats, so things like this are possible:

py> total = 9.5e95 py> term = 1.2 py> total + term == total True

As you can see, term is nothing even close to zero.

So, this example abuses the construct to do something it's not designed to do: perform an unrelated operation before checking the condition.

Well, that's one opinion.

(Cue attempts to squeeze ever mode code here.) I would fail it in review.

Okay.

-- Steve