从主字符串中随机提取等长子字符串

import random

def extract_substrings(main_string, substring_length, num_substrings):
    substrings = []
    
    # 计算主字符串中可能提取的子字符串的数量
    max_start_index = len(main_string) - substring_length
    
    for _ in range(num_substrings):
        # 生成随机的起始位置
        start_index = random.randint(0, max_start_index)
        
        # 提取子字符串并添加到结果列表中
        substring = main_string[start_index:start_index+substring_length]
        substrings.append(substring)
    
    return substrings

# 示例用法
main_string = "This is a sample string."
substring_length = 5
num_substrings = 3

result = extract_substrings(main_string, substring_length, num_substrings)
print(result)