[Python-Dev] PEP 495 accepted (original) (raw)

Guido van Rossum guido at python.org
Tue Sep 22 22:29:37 CEST 2015

Yeah, sadly the point where we should have made this clean break was in 3.0. That's where e.g. inequalities between a string and a number, or between either type and None, were changed from returning something "arbitrary but stable" into raising TypeError. It's much harder to break it now, even with endless deprecation warnings. We might want to try again in 4.0. :-)

On Tue, Sep 22, 2015 at 1:25 PM, Tim Peters <tim.peters at gmail.com> wrote:

[Guido] >> it is broken, due to the confusion about classic vs. timeline arithmetic >> -- these have different needs but there's only one > operator.

[Alex] > I feel silly trying to defend a design against its author. :-) "Design" may be an overstatement in this specific case ;-) I remember implementing this stuff, getting to the comparison operators, and noting that the spec was silent about what to do in case the tzinfos differed. I looked at Guido and explained that, and asked "so whaddya wanna do?". One of us (I don't recall which) said "well, we could convert to UTC first - that would make sense". "Ya, sure," said the other. And I said "and then, of course, interzone subtraction should do the same." "Of course," said Guido, now annoyed that I was bothering him with the obvious ;-) Note that, near that time, Python blithely compared any two objects, even if of wildly different types. Compared to that, doing anything arguably sane with datetime objects seemed wildly desirable. Ironically, the datetime implementation was Python's first library type to refuse to compare its objects to others of wildly different types. So, in all, I'd say well under a minute's thought - between us - went into this decision. And we've been living in Paradise ever since :-)

> Yes, a language with more than one > symbol would not have some > of these problems. Similarly a language with a special symbol for > string catenation would not have a non-commutative + and non- > distributive *. All I am saying is that I can live with the choices made > in datetime. Given that the alternative is suicide, I approve of that life decision.

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