Python handles globals badly.

Antoon Pardon antoon.pardon at rece.vub.ac.be
Mon Sep 14 10:30:18 CEST 2015


Op 12-09-15 om 05:48 schreef Steven D'Aprano:
> I believe I already acknowledged that assignment-as-expression was fine if
> it avoided the = versus == error, from the perspective of avoiding errors.
> But from the perspective of a clean and logical programming model, perhaps
> not so much. Assignment is imperative, not functional, and requiring it to
> return a result is somewhat unclean.

I thought practicallity beats purity? AFAICS python doesn't use such a clean
and logical programming model and it isn't given much critique over it.
So I don't think it is fair to critique assignment as an expression because
of this aspect.

> Look at it this way: suppose you had a robot servant that always, without
> fail or misunderstanding, did what you instructed. There are broadly two
> sorts of things that you can give as instructions: questions, and commands.
> Questions always require an answer: "What's the length of this list?" is
> functional. Commands are imperative, not functional, and don't necessarily
> require an answer: "Move the small red pyramid onto the large green cube."
> Some commands arguable might require an answer, but arguable they are
> better served by an out-of-band error condition (an exception). *Requiring*
> all commands to give an answer is silly, given that the robot servant is
> infallible.

But we are not talking about all commands, we are just talking about assignments.
Sure an assignment has a side effect. But so has ls.pop(). So something having
a side-effect and a value is not unheard of even within a python context.

-- 
Antoon Pardon



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