Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> writes:
> But perhaps we only care about changes in value, not type. NAN or no NAN,
> list equality works fine:
>
> py> data = [1.0, 2.0, float('nan'), 4.0]
> py> old = data[:]
> py> old == data # No changes made yet, should return True
> True
You lost me right here. If list equality is determined by comparing
lists element-by-element, and the second element of old is _not_ equal
to the second element of data, then why should old and data be equal?
In fact, I find myself puzzled about exactly how list equality is
actually defined. Consider:
>>> a = float('nan')
>>> x = [1, a, 9]
>>> y = [1, a, 9.0]
>>> x == y
True
So is there some equality predicate where corresponding elements of x
and y are equal?
>>> map(operator.eq, x, y)
[True, False, True]
It's not "==".
>>> map(operator.is_, x, y)
[True, True, False]
And it's not "is".
--
Alan Bawden
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