为什么当字典有键时会出现 KeyError ？

Question

我正在创建一个简单的烧瓶应用程序来存储 JSON 文件并读取它们。 该应用程序应返回我作为测试制作的 JSON 文件。 这是网址：http://IP:5000/?room=test&game=test。 我收到此错误：

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/lib/python3/dist-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/pi/Desktop/python/universalgameserver.py", line 10, in api_set
    return json.loads(readJSON(request.args['room'], request.args['game']))
  File "/home/pi/Desktop/python/universalgameserver.py", line 17, in readJSON
    f = open("~/saves/${room}_${game}.json".format(room, game), "r")
KeyError: 'room'

打印出字典，看起来是这样的：
{'room': 'test', 'game': 'test'}
我的代码如下所示：

from flask import Flask, request
import json
app = Flask(__name__)
@app.route("/", methods=["GET", "POST"])
def api_set():
    if request.method == "POST":
        writeJSON(request.form['room'], request.form['game'], request.form['json'])
    else:
        print(dict(request.args))
        return json.loads(readJSON(request.args['room'], request.args['game']))

def writeJSON(room, game, json):
    f = open("~/saves/${room}_${game}.json".format(room, game), "w")
    f.write(json)
    f.close()
def readJSON(room, game):
    f = open("~/saves/${room}_${game}.json".format(room, game), "r")
    contents = f.read()
    f.close()
    return contents
if __name__ == '__main__':
    app.run(host='192.168.0.36')

Answer 1

该KeyError是引发readJSON的格式化时：

f = open("~/saves/${room}_${game}.json".format(room, game), "r")

将其更改为：

如果在 Python 2 中：

f = open("~/saves/{0}_{1}.json".format(room, game), "r")

如果在 Python 3.6 或更新版本中，使用 f-string 可以让您轻松格式化：

f = open(f"~/saves/{room}_{game}.json", "r")

它会像魔术一样发挥作用！

聚苯乙烯

同样， writeJSON也发生了变化。