python - 溢出错误 : (34, 'Result too large' )

Question

我遇到溢出错误(OverflowError: (34, 'Result too large')
我想计算 pi 到 100 位小数，这是我的代码:

def pi(): 
    pi = 0 
    for k in range(350): 
        pi += (4./(8.*k+1.) - 2./(8.*k+4.) - 1./(8.*k+5.) - 1./(8.*k+6.)) / 16.**k 
    return pi 
print(pi())

Answer 1

Python float 既不是任意精度也不是无限大小。当 k = 349 时，16.**k 太大了 - 几乎是 2^1400。幸运的是，decimal 库允许任意精度并且可以处理大小:

import decimal
decimal.getcontext().prec = 100
def pi():
    pi = decimal.Decimal(0)
    for k in range(350):
        pi += (decimal.Decimal(4)/(decimal.Decimal(8)*decimal.Decimal(k+1))...)