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

Terry Reedy tjreedy at udel.edu
Thu Jul 5 01:02:37 EDT 2018

On 7/4/2018 1:50 PM, Yury Selivanov wrote:

On Wed, Jul 4, 2018 at 1:35 PM Ivan Pozdeev via Python-Dev <python-dev at python.org> wrote:

On 04.07.2018 11:54, Serhiy Storchaka wrote:

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

This code looks clever that the original while loop with a break in a middle. I like clever code. But it needs more mental efforts for understanding it. I admit that this is a good example. There is a tiny problem with it (and with rewriting a while loop as a for loop, as I like). Often the body contains not a single break. In this case the large part of cleverness is disappeared. :-( It took me a few minutes to figure out that this construct actually checks term == 0.

No. Floats are not reals.

The test is that term is small enough relative to the current total that we should stop adding more terms.

1e50 + 1e30 == 1e50 True

1e30 in not 0 ;-)

Wow, I gave up on this example before figuring this out (and I also stared at it for a good couple of minutes). Now it makes sense. It's funny that this super convoluted snippet is shown as a good example for PEP 572. Although almost all PEP 572 examples are questionable.

-- Terry Jan Reedy

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