Python Flask ValueError：查看函数没有返回响应[重复]

Question

这是我的 Flask 代码：

from flask import Flask
from flask import request

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def signal():
    if request.method == 'POST':
        content = request.get_json()
        return content
    else:
        return 'Hello, world!'

if __name__ == '__main__':
    app.run(debug=True)

我运行这个 HTTP Post（从同一台机器）：

import requests
import json
dump= '{"on":"true"}'
r = requests.post('http://127.0.0.1:5000', dump)

并收到此错误：

[2017-03-04 14:18:35,250] ERROR in app: Exception on / [POST]
Traceback (most recent call last):
File "c:\users\andrew\appdata\local\programs\python\python35-32\lib\site-packages\flask\app.py", line 1982, in wsgi_app
response = self.full_dispatch_request()
File "c:\users\andrew\appdata\local\programs\python\python35-32\lib\site-packages\flask\app.py", line 1615, in full_dispatch_request
return self.finalize_request(rv)
File "c:\users\andrew\appdata\local\programs\python\python35-32\lib\site-packages\flask\app.py", line 1630, in finalize_request
response = self.make_response(rv)
File "c:\users\andrew\appdata\local\programs\python\python35-32\lib\site-packages\flask\app.py", line 1725, in make_response
raise ValueError('View function did not return a response')
ValueError: View function did not return a response

关于为什么会发生这种情况的任何想法？一开始在网上看，以为是因为没有else，万一是GET，但现在看不懂了。

Answer 1

如果你正在测试直接返回你的 post 请求负载，你应该做 jsonify 并且 flask 有这个 util 函数

from flask import Flask
from flask import request, jsonify

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def signal():
    if request.method == 'POST':
        content = request.get_json()
        return jsonify(content)
    else:
        return 'Hello, world!'

if __name__ == '__main__':
    app.run(debug=True)

然后在您的测试代码中，将Content-Type 添加到标题中，（没有这个，request.get_json() 将不起作用）：

dump = '{"on":"true"}'
r = requests.post('http://127.0.0.1:5000', data=dump,
                  headers={'Content-Type': 'application/json'})

Answer 2

看起来 - 问题在于您的脚本正在向您的应用程序发出请求。尝试使用 curl，如下所示：

$ curl -H "Content-type: application/json" -X POST http://127.0.0.1:5000 -d '{"on":"true"}'

你会得到如下回复：

{
  "on": "true"
}

您的代码（添加 jsonify）应如下所示：

from flask import Flask
from flask import request,jsonify 

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def signal():
    if request.method == 'POST':
        content = request.json
        return jsonify(content)
    else:
        return 'Hello, world!'

if __name__ == '__main__':
    app.run(debug=True)