我正在尝试使用zippopotam.us获取特定城市的邮政编码。我有下面的代码可以正常工作，但是当我尝试访问post code返回的密钥时TypeError: expected string or buffer

r = requests.get('http://api.zippopotam.us/us/ma/belmont')
j = r.json()

data = json.loads(j)

print j['state']
print data['places']['latitude']

完整的JSON输出：

{
"country abbreviation": "US",
"places": [
    {
        "place name": "Belmont",
        "longitude": "-71.4594",
        "post code": "02178",
        "latitude": "42.4464"
    },
    {
        "place name": "Belmont",
        "longitude": "-71.2044",
        "post code": "02478",
        "latitude": "42.4128"
    }
],
"country": "United States",
"place name": "Belmont",
"state": "Massachusetts",
"state abbreviation": "MA"
}

谢谢你的帮助。