Python:从文件编辑JSON项目

import json
with open("prefix.json", 'r+') as f:
    data = json.load(f)
def changeprefix(id, prefix):
    global data
    if not id in data:
        json.dump(data, open("prefix.json", "w"), indent = 4)
        data[id] = prefix
    else:
        // Code to edit existing item
changeprefix("6", "?")

(Example.json)
{
    "item": "234"
}