python3 round_python3中为什么 round(0.5) == 0
问题
The behavior of round() for floats can be surprising: for example, round(2.675, 2) gives 2.67 instead of the expected 2.68. This is not a bug: it’s a result of the fact that most decimal fractions can’t be represented exactly as a float. See Floating Point Arithmetic: Issues and Limitations for more information.
▲▲附赠
使用python3实现真四舍五入round()函数代码
#! /usr/bin/env python3
# -*- coding: utf-8 -*-
def trueround(number, places=0):
'''
trueround(number, places)
example:
>>> trueround(2.55, 1) == 2.6
True
uses standard functions with no import to give "normal" behavior to
rounding so that trueround(2.5) == 3, trueround(3.5) == 4,
trueround(4.5) == 5, etc. Use with caution, however. This still has
the same problem with floating point math. The return object will
be type int if places=0 or a float if places=>1.
number is the floating point number needed rounding
places is the number of decimal places to round to with '0' as the
default which will actually return our interger. Otherwise, a
floating point will be returned to the given decimal place.
Note: Use trueround_precision() if true precision with
floats is needed
GPL 2.0
copywrite by Narnie Harshoe
'''
place = 10**(places)
rounded = (int(number*place + 0.5if number>=0 else -0.5))/place
if rounded == int(rounded):
rounded = int(rounded)
return rounded
def trueround_precision(number, places=0, rounding=None):
'''
trueround_precision(number, places, rounding=ROUND_HALF_UP)
Uses true precision for floating numbers using the 'decimal' module in
python and assumes the module has already been imported before calling
this function. The return object is of type Decimal.
All rounding options are available from the decimal module including
ROUND_CEILING, ROUND_DOWN, ROUND_FLOOR, ROUND_HALF_DOWN, ROUND_HALF_EVEN,
ROUND_HALF_UP, ROUND_UP, and ROUND_05UP.
examples:
>>> trueround(2.5, 0) == Decimal('3')
True
>>> trueround(2.5, 0, ROUND_DOWN) == Decimal('2')
True
number is a floating point number or a string type containing a number on
on which to be acted.
places is the number of decimal places to round to with '0' as the default.
Note: if type float is passed as the first argument to the function, it
will first be converted to a str type for correct rounding.
GPL 2.0
copywrite by Narnie Harshoe
'''
from decimal import Decimal as dec
from decimal import ROUND_HALF_UP
from decimal import ROUND_CEILING
from decimal import ROUND_DOWN
from decimal import ROUND_FLOOR
from decimal import ROUND_HALF_DOWN
from decimal import ROUND_HALF_EVEN
from decimal import ROUND_UP
from decimal import ROUND_05UP
if type(number) == type(float()):
number = str(number)
if rounding == None:
rounding = ROUND_HALF_UP
place = '1.'
for i in range(places):
place = ''.join([place, '0'])
return dec(number).quantize(dec(place), rounding=rounding)
本文来自互联网用户投稿，文章观点仅代表作者本人，不代表本站立场，不承担相关法律责任。如若转载，请注明出处。 如若内容造成侵权/违法违规/事实不符，请点击【内容举报】进行投诉反馈！