这是该decimal包中的“真实世界”示例：
>>> from decimal import Decimal
>>> obj = Decimal('3.1415926535897932384626433832795028841971')
>>> +obj != obj # The __pos__ function rounds back to normal precision
True
>>> obj
Decimal('3.1415926535897932384626433832795028841971')
>>> +obj
Decimal('3.141592653589793238462643383')
602392714
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