BLE GATT服务是指蓝牙低功耗（BLE）设备中的Generic Attributes（通用属性）透传协议。可通过该协议读取或写入设备本地缓存。下面是一个Python中使用BLE GATT服务的示例代码：

import bluepy.btle as btle

address = '00:11:22:33:44:55'
BLE_SERVICE_UUID = 'a000'
HANDLE = 0x10

# 连接到设备并获取服务
peripheral = btle.Peripheral(address)
service = peripheral.getServiceByUUID(BLE_SERVICE_UUID)

# 从服务中获取特征
char = service.getCharacteristics()[0]

# 读取值
value = char.read()

# 写入值
char.write(b'Hello World')

# 设置回调函数
def callback(handle, value):
    print("Handle: {}, Value: {}".format(handle, value))

peripheral.withDelegate(MyDelegate(callback))

以上就是使用Python中的bluepy库来读取或写入BLE GATT服务的示例代码。