[Python-Dev] The new and improved PEP 572, same great taste with 75% less complexity! (original) (raw)

Larry Hastings larry at hastings.org
Thu Apr 26 14:07:05 EDT 2018

On 04/26/2018 06:27 AM, Kirill Balunov wrote:

Not sure, but if additional motivating examples are required, there is a common pattern for dynamic attribute lookup (snippet from copy.py):

reductor = dispatchtable.get(cls) if reductor: rv = reductor(x) else: reductor = getattr(x, "reduceex", None) if reductor: rv = reductor(4) else: reductor = getattr(x, "reduce", None) if reductor: rv = reductor() else: raise Error("un(shallow)copyable object of type %s" % cls) which can with the current binding expression syntax simplified to: if reductor := dispatchtable.get(cls): rv = reductor(x) elif reductor := getattr(x, "reduceex", None): rv = reductor(4) elif reductor := getattr(x, "reduce", None): rv = reductor() else: raise Error("un(shallow)copyable object of type %s" % cls) which becomes much clearer, at least in my opinion.

I hate to be pedantic--there's enough of that going on in this thread--but I can't agree with the word "simplifed" above.  I agree that the code using binding expressions is /shorter./  But considering that emit the two code examples implement the exact same algorithm, to the point where their bytecode would look nearly* identical, ISTM that the two code examples are of identical /complexity./

Comparing the two, the code using the binding expressions obviates four newlines, three uses of the identifier "reductor", and allows folding two "else / if"s into "elif"s.  In exchange, it adds three extra colons, and the density of complexity per line has shot up. Whether or not that's an improvement is in the eye of the beholder, and I gather the battle lines around this PEP have already been clearly drawn.  But it cannot be said that this transformation has made the code simpler.

Personally, I've already voted -1; I don't see the version using the binding expressions as an improvement.  Expressing the same code using slightly fewer characters doesn't justify adding syntax to the language in my opinion.

//arry/

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