python函数习题

这些是Python函数的一些习题，请参考下面的解答：

1. 编写一个函数，计算斐波那契数列的前n项和。

def fibonacci_sum(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        fib_list = [0, 1]
        for i in range(2, n+1):
            fib_list.append(fib_list[i-1] + fib_list[i-2])
        return sum(fib_list)

result = fibonacci_sum(n)
print("斐波那契数列的前n项和为:", result)

2. 编写一个函数，实现折半查找。

def binary_search(arr, target):
    low = 0
    high = len(arr) - 1

    while low <= high:
        mid = (low + high) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            low = mid + 1
        else:
            high = mid - 1

    return -1

arr = [0, 1, 2, 11, 20, 101]
target = 20
index = binary_search(arr, target)
print("在数组中的位置索引为:", index)

3. 编写一个函数，反转输入字符串中的字符，但保持标点符号不变。

def reverse_string(s):
    punctuation = '''!()-[]{};:'"\,<>./?@#$%^&*_~'''
    words = s.split()
    reversed_words = []

    for word in words:
        if len(word) > 1 and any(char not in punctuation for char in word):
            reversed_word = word[::-1]
            reversed_words.append(reversed_word)
        else:
            reversed_words.append(word)

    return ' '.join(reversed_words)

string = "I enjoy reading!"
reversed_string = reverse_string(string)
print("颠倒后的字符串为:", reversed_string)