回答編集履歴
1
追記
answer
CHANGED
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@@ -11,4 +11,25 @@
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11
11
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ctx.rounding = decimal.ROUND_FLOOR # -∞方向に丸める ≒ 切り捨て
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12
12
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v = round(decimal.Decimal(v), 3) # 3桁, FLOORモードで丸め
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13
13
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print('{}'.format(v)) # -> 1.888
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14
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-
```
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14
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```
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15
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16
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--- 追記
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17
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改めた点はlocalcontext()/round()を使わず、quantize()メソッドにしたこと。それと負の場合に切り捨てにならないので、ROUND_DOWNに変更しています。動作確認はPython3.5.1とPython2.7.11。
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18
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```python
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19
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from decimal import (Decimal, ROUND_DOWN)
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20
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21
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def round_down3(value):
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22
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value = Decimal(value).quantize(Decimal('0.001'), rounding=ROUND_DOWN)
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23
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return str(value)
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24
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25
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print(round_down3(188888.8888888))
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26
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print(round_down3(1.8888899999))
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27
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print(round_down3(0.9999999999))
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28
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print(round_down3(-1.9999999999))
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29
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30
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# 出力
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31
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# 188888.888
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32
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# 1.888
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33
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# 0.999
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34
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# -1.999
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35
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```
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