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这样计算pi的速度会不会太慢了

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Kube仔-

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def pi(N): ' 计算pi的值 '

# step 1: 创建一个奇数序列: 1, 3, 5, 7, 9, ...
natuals = itertools.count(1, 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, natuals)
# step 3: 添加正负符号并用4除: 4/1, -4/3, 4/5, -4/7, 4/9, ...
ns = map(lambda n: 4/n * (1 if n % 4 == 1 else -1), ns)
# step 4: 求和:
return reduce(lambda a,b: a+b, ns)

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