[Python-Dev] Order of positional and keyword arguments (original) (raw)

Chris Jerdonek chris.jerdonek at gmail.com
Fri Apr 27 05:46:27 EDT 2018

On Thu, Apr 26, 2018 at 12:25 PM, Serhiy Storchaka <storchaka at gmail.com> wrote:

f(b=2, *[1]) is surprised in two ways:

1. Argument values are passed not in order. The first value is assigned to the second parameter, and the second value is assigned to the first parameter. 2. Argument values are evaluated not from left to right. This contradicts the general rule that expressions are evaluated from left to right (with few known exceptions). I never seen the form f(b=2, *[1]) in practice (though the language reference contains an explicit example for it), and it looks weird to me. I don't see reasons of writing f(b=2, *[1]) instead of more natural f(*[1],_ _b=2). I propose to disallow it.

Coincidentally, I recently came across and reviewed a PR to Django that proposed exactly this, or at least something very similar. They proposed changing--

def create_cursor(self, name=None):

to-- def create_cursor(self, name=None, *args, **kwargs):

https://github.com/django/django/pull/9674/files#diff-53fcf3ac0535307033e0cfabb85c5301R173

--Chris

This will also make the grammar simpler. Current grammar: argumentlist: positionalarguments ["," starredandkeywords] : ["," keywordsarguments] : | starredandkeywords ["," keywordsarguments] : | keywordsarguments positionalarguments: [""] expression ("," [""] expression)* starredandkeywords: ("*" expression | keyworditem) : ("," "" expression | "," keyworditem) keywordsarguments: (keyworditem | "**" expression) : ("," keyworditem | "," "**" expression)* keyworditem: identifier "=" expression Proposed grammar: argumentlist: positionalarguments ["," keywordsarguments] : | keywordsarguments positionalarguments: [""] expression ("," [""] expression)* keywordsarguments: keywordargument ("," keywordargument)* keywordargument: identifier "=" expression | "**" expression

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