嵌套字典断言，返回错误"TypeError:列表索引必须是整数，而不是字符串“

my_dict = {
    'key1': {
        'nested_key1': 'value1',
        'nested_key2': 'value2'
    },
    'key2': {
        'nested_key3': 'value3',
        'nested_key4': 'value4'
    }
}

# 检查键是否存在后再进行操作
if 'key1' in my_dict and 'nested_key1' in my_dict['key1']:
    nested_value = my_dict['key1']['nested_key1']
    print(nested_value)
else:
    print('Key or nested key does not exist')

# 使用try-except语句捕获异常
try:
    nested_value = my_dict['key1']['nested_key1']
    print(nested_value)
except KeyError:
    print('Key or nested key does not exist')