def pi(N): #' 计算pi的值 ' # step 1: 创建一个奇数序列: 1, 3, 5, 7, 9, ... od = itertools.count(1,step=2) # step 2: 取该序列的前N项: 1, 3, 5, 7, 9, ..., 2*N-1. Ns = itertools.takewhile(lambda x:x<=2*N-1, od) # step 3: 添加正负符号并用4除: 4/1, -4/3, 4/5, -4/7, 4/9, ... mN = map(lambda x:((-1)**(x//2))*4/x,Ns) # step 4: 求和: return sum(mN)
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