def pi(N):    """ 计算pi的值 """    # # step 1: 创建一个奇数序列: 1, 3, 5, 7, 9, ...    # odd_list = itertools.count(1, 2)  # 1开始 步长为2    # # step 2: 取该序列的前N项: 1, 3, 5, 7, 9, ..., 2*N-1.    # odds = itertools.takewhile(lambda x: x <= 2 * N - 1, odd_list)    odds = (x * 2 + 1 for x in range(N))    # step 3: 添加正负符号并用4除: 4/1, -4/3, 4/5, -4/7, 4/9, ...    symbol = itertools.cycle([1, -1])    # step 4: 求和:    sum = 0    for i in odds:        sum += 4 * next(symbol) / i    return sum# 测试:print(pi(10))print(pi(100))print(pi(1000))print(pi(10000))assert 3.04 < pi(10) < 3.05assert 3.13 < pi(100) < 3.14assert 3.140 < pi(1000) < 3.141assert 3.1414 < pi(10000) < 3.1415print('ok')