[Tutor] Hummm...dubious behavior.

[alan.gauld@bt.com]

> >>> 0.6125
> 0.61250000000000004
> >>>
> 
> occurs because of the fact, that the number 0.6125 
> is not a power of 2 (or 1/2) and so the internal 
> binary representation of it *has* to be
> an approximation of it.

Correct. And round is not intended to change the 
printed representation of the numbers but to change 
the actual value of the number.

To change the representation use string formatting 
codes

Thus:

>>> print "%5.3" % math.pi
3.142

ie 5 characters with 3 after the decimal point.

> (Maybe this has something to do with the difference
> between __repr__ and __str__   (?) )

Yes again. The interpreter uses one, print uses the other.
(I can't remember which is which, I thing print uses str...)

> >>> print 0.6125, 4.1225
> 0.6125 4.1225                  
> >>> print (0.6125, 4.1225)
> (0.61250000000000004, 4.1224999999999996)

No, its consistent, one is the __str__ of a number the 
other is the __str__  of a tuple. Its down to how those 
__str__ functions work not a discrepency in print.

[ You should be able to verify this by calling the 
__str__ and __repr__ functions explicitly, but 
I haven't tried... ]

Alan g.
Author of the 'Learning to Program' web site
http://www.freenetpages.co.uk/hp/alan.gauld