Python前n项和

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构造函数并调用，垃圾大学生明天就要考这个了，求解答，急！非常急！

感谢大家的解答，评论区的答案我还没有试过，贴上我试过正确的答案

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def calculate_sum(n):
    sum = 0.0
    sign = 1.0
    numerator = 1.0
    denominator = 2.0
    for i in range(n):
        term = sign * numerator / denominator
        sum += term
        sign *= -1.0
        numerator += 1.0
        denominator += numerator
    return sum

n = int(input())
result = calculate_sum(n)
print("前{}项的和为：{:.6f}".format(n, result))




# 请在这里输入代码
n = int(input())
sum = 0.0
for i in range(1, n+1):
    if i % 2 == 1:
        sign = 1 
    else:
        sign = -1
    sum += sign*i/(2*i-1)
print(format(sum, '.6f'))