python 里3.15 round(3.15,1)=3.1
print(round(3.15,1))
decimal.getcontext().rounding=decimal.ROUND_HALF_UP
b=decimal.Decimal('3.15',decimal.getcontext())
print(round(b,1))
python 里3.15 round(3.15,1)=3.1
print(round(3.15,1))
decimal.getcontext().rounding=decimal.ROUND_HALF_UP
b=decimal.Decimal('3.15',decimal.getcontext())
print(round(b,1))