Decimals not equalling themselves (e.g. 0.2 = 0.2000000001)

Gabriel Genellina gagsl-py2 at
Tue Aug 5 19:37:47 CEST 2008

En Tue, 05 Aug 2008 11:50:43 -0300, schinckel <matt at> escribió:

> I had a class today which dealt with Decimal <-> IEE754 conversion,
> and
> whilst 0.1 was an example that was converted, and a representation was
> generated, no mention was made of the precision issue.
> I'm hoping that it was just that we ran out of time, and the lecturer
> will discuss it in detail next time.

Presumably you encountered that 0.1 (decimal) = 0.000110011001100... (binary), and as you can see it has infinite periodic bits. IEEE754 stores only a finite number of bits for the mantissa, all the remaining (infinite) bits are dropped; a representation error is unavoidable.

Gabriel Genellina

More information about the Python-list mailing list