flask: request.json always returns none despite of sending valid json

Question

i have this code on server side

from flask import Flask, request, jsonify

app=Flask(__name__)

@app.route("/pingtest")
def pingtest():
    return "Pong!"

@app.route("/registrar_alumno", methods=["POST"])
def registrar_alumno():
    print(request.json)
    return jsonify(request.json)

app.run(debug=True,port=4000)

and on the client i have this code

import requests

r=requests.post("http://127.0.0.1:4000/registrar_alumno",
    data={"test":"hello there"})
print(r.text)

i expect to obtain {"test":"hello there"} in both sides but i have this on server:

(asistencias) PS C:\Users\Alumno\Desktop\Proyectos\py\gestion_academica\asistencias> python .\server.py [...] (irrelevants messages that server always shows)

None #...(this should be print(request.json) instruction)

127.0.0.1 - - [15/Mar/2020 16:22:45] "←[37mPOST /registrar_alumno HTTP/1.1←[0m" 200 -

and this on client

(asistencias) PS C:\Users\Alumno\Desktop\Proyectos\py\gestion_academica\asistencias> python .\testclient.py

None

i have no idea what's wrong with this, i hope someone can help me to found the bug

Answer 1

This is happening because you are using the data parameter with a dictionary in your client request which sends form-encoded data, causing request.json to return None.

Use the json parameter to send JSON:

import requests

r=requests.post("http://127.0.0.1:4000/registrar_alumno", json={"test":"hello there"})

This will serialize the data as JSON and change the Content-Type header to application/json.

See the requests docs on more complicated POST requests.