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Comment by commenter23 | Hacker News Reader

The point the article makes on comparing floating point values and the floating point type is true, but it's not because of any rounding error.

It's because the comparison operators are defined for every value. That is, "True < []" is valid in Python 2.7, along with any other 2 values, regardless of type. This is a surprising instance of weak typing in Python, which is otherwise strongly typed, which is why this was fixed in Python 3 (https://docs.python.org/3.0/whatsnew/3.0.html#ordering-compa...).

This is also not a case of Python doing something useful, like with '"foo"*2'. The result of the comparison is defined, but it's not useful. I suppose it was useful for making sure that you can always sort a list, but there are better ways to do that.

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> The point the article makes on comparing floating point values and the floating point type is true, but it's not because of any rounding error.

Do you mean this example? (it's the only one I can find about floating point comparison)

> 2.2 * 3.0 == 3.3 * 2.0

It's definitely due to accuracy error. (rather than type comparison) How would you explain it otherwise?

Accuracy problems in floating-point computations: https://en.wikipedia.org/wiki/Floating_point#Accuracy_proble...

My bad, wrote rounding not accuracy. (corrected now) But my point was that it's not related to weak typing as the parent seems to suggest.

> But my point was that it's not related to weak typing as the parent seems to suggest.

And you're completely right there. Any language using floating-point numbers will have the same issue regardless of its typing discipline e.g. Rust: https://is.gd/4BNoWa

There is another snippet near that section which evaluates the following.

    >>> float > float('infinity')
    True

Bah, you're right, missed that example :(

This really makes me wish they made the decision for Python 3 to auto-convert these literals to Fraction objects like Perl 6 does.

Basically, autoconvert the above to this (and make Fraction a builtin instead of in the standard library, of course):

    >>> Fraction('2.2') * Fraction('3.0') == Fraction('3.3') * Fraction('2.0')
    True

The speed of these operations isn't on the same order of magnitude as floating-point operations. I do agree that literals for `Fraction` and `Decimal` would be interesting.

Also, I think that '2.2' is better represented as `Decimal`, as it's a decimal number (which is a subset of rational numbers, that are usually better represented using `Decimal`) (edit: that of course depends on the use case, as Decimal uses fixed-point precision).

> not ... something useful

Intertype comparison is useful for sorting a list of heterogenous types. But for Python 3 they decided that use case wasn't so important.

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