Mailman 3 Fwd: Make `float('inf') //1 == float('inf')` - Python-ideas

17 Sep 2014

      ---------- Forwarded message ----------
From: Ian Cordasco 
Date: Wed, Sep 17, 2014 at 4:51 PM
Subject: Re: [Python-ideas] Make `float('inf') //1 == float('inf')`
To: Ram Rachum 
Cc: "python-ideas@googlegroups.com" 

On Wed, Sep 17, 2014 at 11:42 AM, Ram Rachum  wrote:
...
Please see this discussion on python-list:
https://groups.google.com/forum/#!topic/comp.lang.python/maDZoc-n4bA
Currently `float('inf') //1` is equal to NaN. I think that this is really
weird. If I understand correctly it's to maintain the invariant `div*y + mod
== x`. The question is, do we really care more about maintaining this
invariant rather than providing a mathematically reasonable value for floor
division?
Actually there are 2 things here:

1. Mathematically speaking, infinity is a real number and modulo
arithmetic is algebraically not defined for it. So the "mathematically
reasonable value" is NaN. Is it intuitive for someone who hasn't
studied abstract algebra? Probably not. Is it functional for the
scientific python community? Almost certainly although I won't pretend
to speak on their behalf

2. Changing this behaviour is not something I think we should do in a
minor version of 3.4 or in 3.5 (or really 3.x).

Fwd: Make `float('inf') //1 == float('inf')`

Ian Cordasco

tags

participants (10)