def pi(N): ' 计算pi的值 ' # step 1: 创建一个奇数序列: 1, 3, 5, 7, 9, ... n = itertools.count(start = 1, step = 2) # step 2: 取该序列的前N项: 1, 3, 5, 7, 9, ..., 2*N-1. n = itertools.takewhile(lambda x: x <= 2 * N - 1, n) # step 3: 添加正负符号并用4除: 4/1, -4/3, 4/5, -4/7, 4/9, ... d, s = 4, 0 for v in n: s += d / v d *= -1 # step 4: 求和: return s
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