要访问JSON代码中的嵌套值，可以使用点号（.）或方括号（[]）来访问对象属性或数组元素。

下面是一个JSON代码的示例：

{
  "name": "John",
  "age": 30,
  "address": {
    "street": "123 Main St",
    "city": "New York"
  },
  "hobbies": ["reading", "running", "painting"]
}

以下是几种访问嵌套值的方法：

1. 使用点号（.）来访问对象属性：

import json

data = '''
{
  "name": "John",
  "age": 30,
  "address": {
    "street": "123 Main St",
    "city": "New York"
  },
  "hobbies": ["reading", "running", "painting"]
}
'''

json_data = json.loads(data)

name = json_data["name"]
street = json_data["address"]["street"]
city = json_data["address"]["city"]

print(name)    # 输出: John
print(street)  # 输出: 123 Main St
print(city)    # 输出: New York

2. 使用方括号（[]）来访问对象属性或数组元素：

import json

data = '''
{
  "name": "John",
  "age": 30,
  "address": {
    "street": "123 Main St",
    "city": "New York"
  },
  "hobbies": ["reading", "running", "painting"]
}
'''

json_data = json.loads(data)

name = json_data["name"]
street = json_data["address"]["street"]
city = json_data["address"]["city"]
hobby = json_data["hobbies"][0]

print(name)    # 输出: John
print(street)  # 输出: 123 Main St
print(city)    # 输出: New York
print(hobby)   # 输出: reading

无论是使用点号还是方括号，都可以访问JSON代码中的嵌套值。