如何从此json字符串中删除花括号前的双引号

import json

# 给定的JSON字符串
json_str = '{"name": "John", "age": 30}'

# 解析JSON字符串
data = json.loads(json_str)

# 删除花括号前的双引号
for key in data.keys():
    if isinstance(data[key], str):
        data[key] = data[key].lstrip('"')

# 重新构建JSON字符串
modified_json_str = json.dumps(data)

print(modified_json_str)

{"name": "John, "age": 30}