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Probably this will look non-intuitive, but underlying floating-point
arithmetic is binary, not decimal. Thus, round(x, n) sometimes will pick
up a decimal representation with more than n digits. This is something
common for CPython < 2.7 and < 3.1:
Python 2.6.6 (r266:84292, Aug 12 2014, 07:57:07)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> round(0.42754287856598971, 2)
0.42999999999999999
And with this patch as well:
Python 3.12.5+ (heads/3.12:0181aa2e3e, Aug 29 2024, 14:55:08) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from mpmath import *
>>> round(mp.mpf(0.42754287856598971), 2)
mpf('0.42999999999999999')
>>> mp.pretty = True
>>> round(mp.mpf(0.42754287856598971), 2)
0.43
See also python/cpython#45921
Closes mpmath#455
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I'm going to merge this after a week. But I would appreciate @cbm755 feedback, as new feature might look surprising. |
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Probably this will look non-intuitive, but underlying floating-point arithmetic is binary, not decimal. Thus, round(x, n) sometimes will pick up a decimal representation with more than n digits. This is something common for CPython < 2.7 and < 3.1:
And with this patch as well:
See also python/cpython#45921
Closes #455