Flask：使用POST方法存储值并使用GET方法检索它

Question

I've been working with Flask for quite a bit.

I have an output, just a number which increases or decreases constantly, I want to capture it with flask POST method and, retrieve immediately.

I've created an application to retrieve the latest POST in a GET method using the same context:

cumulative = ['x']
@app.route('/xxx', methods=['GET', 'POST'])
def refresh():
    aexample = request.get_json()
    cumulative.append(aexample)
    return str(cumulative[1]['thing2'])

It works, but if you refresh the page sometimes this error appears in the logs:

TypeError: 'NoneType' object is not subscriptable

In this line:

cumulative.append(aexample)

I've tried using:

cumulative[0] = aexample

But that doesn't work, it says the value is "None". That's why I made it incremental (just for test purposes).

All of this makes me think, storing the latest POST values in a list isn't the smart way to do this.

I've been thinking on using some sort of cache, the posted value changes every minute and I would like to retrieve only the latest posted value. I'm not interested in storing the values permanently.

Is there a good way to do this?

Answer 1

You're probably getting the error from missing request json, on a GET request (ie cumulative[1] is None , so you can't get ['thing2'] ).

To persist between requests, and trusting your data size is not too large, you may be able to store it in session .

Otherwise you may want to look at something more scalable like Redis

Answer 2

Ok, first thanks to @dylanj.nz for pointing my error with the requests.

Finally I've achieved what I wanted, I've created conditionals for both requests, this is the code on flask:

# 'Some Kind of Real Time Stuff'
cumulative = ['x']
@app.route('/xxx', methods=['GET', 'POST'])
def refresh():
    aexample = request.get_json()
    if flask.request.method == 'POST':
        cumulative[0] = str(aexample)
        return 'data received'
    if flask.request.method == 'GET':
        return str(cumulative[0])

[ Using CURL to send data ] Now, sending data to the method:

curl -XPOST -H "Content-Type: application/json" http://someProject/xxx -d '{"thing2":"sdpofkdsofk"}'

[ Apache - Log ]The POST were received successfully:

myapacheserver:80 76.5.153.20 - - [23/Jul/2019:11:02:40 -0400] "POST /xxx HTTP/1.1" 200 182 "-" "curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0 OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3"

[ Apache - Log ] GET works! presenting the latest value:

myapacheserver:80 76.220.156.100 - - [23/Jul/2019:11:03:52 -0400] "GET /xxx HTTP/1.1" 200 327 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0"

This is displayed on the page http://myapacheserver/xxx :

{'thing2': 'sdpofkdsofk'}

Yes, I'm storing the dict as an string, but it works, I'll deal later with the data type.