Chris Angelico <ros...@gmail.com> writes: > On Sat, Nov 20, 2021 at 5:08 AM ast <ast@invalid> wrote:
>> >>> 0.3 + 0.3 + 0.3 == 0.9 >> False > > That's because 0.3 is not 3/10. It's not because floats are > "unreliable" or "inaccurate". It's because the ones you're entering > are not what you think they are. > > When will people understand this? > > (Probably never. Sigh.) Most people understand what's going on when it's explained to them. And I think that being initially baffled is not unreasonable. After all, almost everyone comes to computers after learning that 3/10 can be written as 0.3. And Python "plays along" with the fiction to some extent. 0.3 prints as 0.3, 3/10 prints as 0.3 and 0.3 == 3/10 is True. The language (a language, not Python) could tell you that you were not getting the value you asked for. Every 0.3 could come with a warning that 0.3 can not be represented exactly as a floating point value. To avoid the warning, the programmer would write ~0.3 meaning, exactly, the binary (or whatever the base really is) floating point number closest to 0.3. -- Ben. -- https://mail.python.org/mailman/listinfo/python-list
