Python:使用类型的set count生成字符串组合。(字符串x长度为，x数字，x大写，x小写)

import itertools

def generate_combinations(length):
    digits = set('0123456789')
    uppercase_letters = set('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
    lowercase_letters = set('abcdefghijklmnopqrstuvwxyz')
    
    all_chars = [digits, uppercase_letters, lowercase_letters]
    
    combinations = []
    for combination in itertools.product(*all_chars):
        # Check if the length of the combination meets the requirement
        if len(combination) == length:
            combinations.append(''.join(combination))
    
    return combinations

# Test the function
length = 3
combinations = generate_combinations(length)
print(combinations)