如何从嵌套的字典中生成一个方阵？

def generate_square_matrix(nested_dict):
    # 提取键值对并记录键的数量
    key_value_pairs = list(nested_dict.items())
    n = len(key_value_pairs)
    
    # 创建空方阵
    matrix = [[None] * n for _ in range(n)]
    
    # 填充方阵
    for i, (key, value) in enumerate(key_value_pairs):
        # 计算键的索引
        index = ord(key) - ord('a')
        matrix[index][index] = value
    
    return matrix

# 示例嵌套字典
nested_dict = {
    'a': 1,
    'b': 2,
    'c': 3,
    'd': 4
}

# 生成方阵
matrix = generate_square_matrix(nested_dict)

# 打印方阵
for row in matrix:
    print(row)