Python中的Decimal非常有意思，它最大的特点是：使用它来计算0.1+0.2会得到0.3。大家可能会问，这不很正常么？ 大家可以用用Python内置的数据类型算一下0.1+0.2，结果应该是0.30000000000000004，呵呵。

Decimal号称：

computers must provide an arithmetic that works in the same way as the arithmetic that people learn at school.

示例代码如下：

from decimal import Decimal
a=Decimal('4.2')
b=Decimal('2.1')
print(a+b)
print(4.2+2.1)
print(a+b==Decimal('6.3'))
print(a+b==4.2+2.1)

from decimal import localcontext
a=Decimal('1.3')
b=Decimal('1.7')
print(a/b)
with localcontext() as ctx:
    ctx.prec=3
    print(a/b)
with localcontext() as ctx:
    ctx.prec=50
    print(a/b)

参考资料：

https://docs.python.org/3/library/decimal.html