[Python-Dev] redefining is

[Andrew Koenig]

> So identity means the same object, and implies equivalence.

Yes.

> Equivalence means they will always have the same value, even
> if you do something to one and not the other.  This implies
> (current value) equality.

Yes, unless equality is defined weirdly.  For example, IEEE floating-point
NaN is supposed to be unequal to itself.

> equality just means that they have the same value *now*.

I'm not sure the implication goes the other way.  Consider a string-like
type for which == ignores case.  Then equivalence implies identity, but not
the other way.

> Since equivalence is a stronger form of equality, why not
> just use "===".

Seems plausible.

> Anything that is === will also be ==, but the extra character
> will mark it as special.  If the mark isn't strong enough,
> perhaps "=~="; in math the ~ often modifies equality to mean
> "not identical, but close enough".

I wish.  But unfortunately sometimes x == x is False.

> equal_forever would also work, and be explicit.  equal_forever
> has the additional advantage that it could be written as a
> function rather than an operator during a trial period.

Indeed.  I'd prefer something shorter, though, such as equiv.