python_利用迭代器(生成器）来计算数列的前n项和

有一分数序列：2/1，3/2，5/3，8/5，13/8，21/13…, 分别求出这个数列的前10项之和以及前20项之和，并打印输出，输出格式要求小数点后保留4位。

""" iterator """
def fib_variant(generate_max_times):
    count = 0
    a, b = 2, 3
    while count < generate_max_times:
        yield a
        a, b = b, a+b
        count += 1
    return "end"

def fib_variant2(generate_max_times):
    count = 0
    a, b = 1, 2
    while count < generate_max_times:
        yield a
        a, b = b, a+b
        count += 1
""" test the iterator: """
# for i in fib_variant(10):
#     print(i)
# for i in fib_variant2(10):
#     print(i)
""" calculate:sum: 2/1，3/2，5/3，8/5，13/8，21/13."""
def sum_fib_variant(bound):
    count = 0
    f1 = fib_variant(bound)
    f2 = fib_variant2(bound)

    """ range from 0(not 1) """
    for i in range(0, bound):
        count += next(f1)/next(f2)
        # print(count)
    return count

print("sum_10=%.4f" % sum_fib_variant(10))
print("sum_20=%.4f" % sum_fib_variant(20))