python中的Decimal对象

Question

>>> from decimal import *
>>> amount = Decimal(0.00114206599999999995793953377898333201301284134387969970703125)
>>> sZ = Decimal(0.0001)
>>> amount.quantize(sZ, rounding=ROUND_DOWN)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
decimal.InvalidOperation: [<class 'decimal.InvalidOperation'>]
>>> 
>>> amount = amount - (amount % sZ)
>>> amount
Decimal('0.001100000000000000052713909626')
>>> amount.quantize(sZ, rounding=ROUND_DOWN)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
decimal.InvalidOperation: [<class 'decimal.InvalidOperation'>]
>>> 

我期望得到0.011

有人能解释一下我的例子中python十进制的错误吗？你知道吗

基本上，我只想得到一个数字，它是大量的sZ（chunksize）和四舍五入从'金额'（它可能永远不会更多）。你知道吗

Answer 1

如果您确实关心精度，请执行以下操作：

>>> from decimal import *
>>> amount = Decimal('0.00114206599999999995793953377898333201301284134387969970703125')
>>> sZ = Decimal('0.0001')
>>> amount.quantize(sZ, rounding=ROUND_DOWN)

问题是float有精度问题，将float作为参数传递给Decimal已经失去了精度。你知道吗