Às 23:29 de 11-03-2017, Erik escreveu: > Hi Paulo, > > On 11/03/17 22:01, Paulo da Silva wrote: ...
>> 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? > > Firstly, if the values are changing then they are being first written by > a process that has a very strict decimal representation and then read in > and re-written by something that has a less-strict representation (I'm > guessing that by "float/double values", you mean IEEE 754). I don't know. I can tell you that I'm using pandas data frame read_csv and to_csv to read and write. > > Because IEEE 754 can't represent all values *exactly*, some input values > will change to something close as you have seen. > However, if the input value matches something that IEEE 754 *can* > represent exactly then it will not change. > > Whether you will see _cumulative_ errors depends on whether the output > stage of the first pass truncates the output with a field width > specifier or similar. If not, then you should see the initial change > you've noticed and then nothing more after that for that particular datum. Ok, I like that. > > > Having said all that, if you use Python's decimal.Decimal type instead > of float/double for processing your files, then you are better off if > absolute precision is what you need. No, I don't think it is needed. It will unnecessarily complicate my scripts. They have lots of calculations (matrix like operations). I don't care about fine precision. Only cumulative changes. I was in doubt if the data was going to change over time. Thank you very much. -- https://mail.python.org/mailman/listinfo/python-list
