Chris Angelico <ros...@gmail.com> writes: > Right. Obviously a true 'real number' representation can't be done. > But there are multiple plausible approximations thereof (the best > being rationals).
Sure. But most of those are not what is most commonly meant by ‘float’ type. > Not asking for Python to be changed, just wondering why it's defined > by what looks like an implementation detail. Because, in the case of the ‘float’ type, the agreed-upon meaning of that type – in Python as in just about every other language that is well-specified – is “an IEEE float as per the IEEE 754 spec”. A foolish consistency to the spec would be a hobgoblin for little minds. But, given that a ‘float’ type which deviated from that spec would just be inviting all sorts of other confusion, it's not a foolish consistency. > It's like defining that a 'character' is an 8-bit number using the > ASCII system, which then becomes problematic with Unicode. Right. That's why in Python 3 the Unicode text type is called ‘unicode’, the IEEE float type is called ‘float’, and the byte string type is called ‘bytes’. It's also why the ‘str’ type in Python 2 was painful enough to need changing: it didn't clearly stick to a specification, but tried to straddle the worlds between one specification (a text type) and an incompatible other specification (a bytes sequence type). Where there is a clearly-defined widely-agreed specification for a type, it's a good idea to stick to that specification when claiming to implement that functionality in a type. -- \ “The man who is denied the opportunity of taking decisions of | `\ importance begins to regard as important the decisions he is | _o__) allowed to take.” —C. Northcote Parkinson | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
