[Python-Dev] PEP 572: Assignment Expressions (original) (raw)

Anthony Flury anthony.flury at btinternet.com
Sat Apr 21 04:38:04 EDT 2018

On 21/04/18 08:46, Chris Angelico wrote:

doubleditems = [x for x in (items := getitems()) if x * 2 in items]

This will leak 'items' into the surrounding scope (but not 'x'). At the risk of stating the obvious - wasn't there work in Python 3 to prevent leakage from comprehensions ? [x for x in x if x] # This works [x for y in x if x := y] # UnboundLocalError

The standard library example given earlier notwithstanding, I can see no benefit in using the same name as the iterator and the loop target name. To be honest I have trouble parsing that first version, and keeping track of which x is which (especially which x is being used in the conditional clause) : surely this would be better : [x_item for x_item in x if x_item]

Your 2nd example makes no sense to me as to the intention of the code - the re-use of the name x is confusing at best.

-- Anthony Flury email : Anthony.flury at btinternet.com Twitter : @TonyFlury <https://twitter.com/TonyFlury/>

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