a = 4.2
b = 2.1
a + b
6.300000000000001
(a + b) == 6.3
False
浮点数运算用decimal
from decimal import Decimal
a = Decimal('4.2')
b = Decimal('2.1')
a + b
Decimal('6.3')
print(a + b)
6.3
(a + b) == Decimal('6.3')
True
利用localcontext控制精度
from decimal import localcontext
a = Decimal('1.3')
b = Decimal('1.7')
print(a / b)
0.7647058823529411764705882353
with localcontext() as ctx:
... ctx.prec = 3
... print(a / b)
...
0.765
with localcontext() as ctx:
... ctx.prec = 50
... print(a / b)
...
0.76470588235294117647058823529411764705882352941176
