Precision reading and writing data frames to csv

[MRAB]

On 2017-03-11 22:01, Paulo da Silva wrote:
> Hi!
>
> I have a dir with lots of csv files. These files are updated +- once a
> day. I could see that some values are converted, during output, to very
> close values but with lots of digits. I understand that is caused by the
> internal bits' representation of the float/double values.
>
> Now my question is: Is it possible the occurrence of successive
> cumulative errors? I mean reading a file, adding lines or change few
> ones but keeping the most of the other lines untouched and, even so,
> existent untouched lines keep always changing?
>
If it's writing out _exactly_ what it's reading in, how can it be changing?