mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-07-24 03:35:53 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 8

Remove the round() discussion which is now out-of-date.

Browse source
This commit is contained in:
Raymond Hettinger 2009-04-26 20:10:50 +00:00
parent ce95e5646b
commit f0320c7ee6
1 changed files with 2 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

19
Doc/tutorial/floatingpoint.rst
View file

@ -108,23 +108,8 @@ reproduce *x*, but the output may be more pleasant to look at::
It's important to realize that this is, in a real sense, an illusion: you're
simply rounding the *display* of the true machine value.
Other surprises follow from this one. For example, after seeing ::
>>> format(0.1, '.17g')
'0.10000000000000001'
you may be tempted to use the :func:`round` function to chop it back to the
single digit you expect. But that makes no difference::
>>> format(round(0.1, 1), '.17g')
'0.10000000000000001'
The problem is that the binary floating-point value stored for "0.1" was already
the best possible binary approximation to 1/10, so trying to round it again
can't make it better: it was already as good as it gets.
Another consequence is that since 0.1 is not exactly 1/10, summing ten values of
0.1 may not yield exactly 1.0, either::
One illusion may beget another. For example, since 0.1 is not exactly 1/10,
summing ten values of 0.1 may not yield exactly 1.0, either::
>>> sum = 0.0
>>> for i in range(10):