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

Chris Jerdonek chris.jerdonek at gmail.com
Mon Apr 23 21:42:17 EDT 2018

On Mon, Apr 23, 2018 at 4:54 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

Tim Peters wrote:

if (diff := x - xbase) and (g := gcd(diff, n)) > 1: return g My problem with this is -- how do you read such code out loud?

It could be--

"if diff, which we let equal x - x_base, and g, which ..." or "if diff, which we set equal to x - x_base, and g, which ...." or "if diff, which we define to be x - x_base, and g, which ...." or "if diff, which we define as x - x_base, and g, which ....." etc.

--Chris

From my Pascal days I'm used to reading ":=" as "becomes". So this says: "If diff becomes x - base and g becomes gcd(diff, n) is greater than or equal to 1 then return g." But "diff becomes x - base" is not what we're testing! That makes it sound like the result of x - base may or may not get assigned to diff, which is not what's happening at all. The "as" variant makes more sense when you read it as an English sentence: if ((x - xbase) as diff) and ... "If x - xbase (and by the way, I'm going to call that diff so I can refer to it later) is not zero ..." -- Greg

Python-Dev mailing list Python-Dev at python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/chris.jerdonek%40gmail.com

More information about the Python-Dev mailing list