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Get the data received in a Flask request


Question

I want to be able to get the data sent to my Flask app. I've tried accessing request.data but it is an empty string. How do you access request data?

from flask import request

@app.route('/', methods=['GET', 'POST'])
def parse_request():
    data = request.data  # data is empty
    # need posted data here

The answer to this question led me to ask Get raw POST body in Python Flask regardless of Content-Type header next, which is about getting the raw data rather than the parsed data.

2020/04/07
1
786
4/7/2020 10:44:46 PM

Accepted Answer

The docs describe the attributes available on the request. In most common cases request.data will be empty because it's used as a fallback:

request.data Contains the incoming request data as string in case it came with a mimetype Flask does not handle.

  • request.args: the key/value pairs in the URL query string
  • request.form: the key/value pairs in the body, from a HTML post form, or JavaScript request that isn't JSON encoded
  • request.files: the files in the body, which Flask keeps separate from form. HTML forms must use enctype=multipart/form-data or files will not be uploaded.
  • request.values: combined args and form, preferring args if keys overlap
  • request.json: parsed JSON data. The request must have the application/json content type, or use request.get_json(force=True) to ignore the content type.

All of these are MultiDict instances (except for json). You can access values using:

  • request.form['name']: use indexing if you know the key exists
  • request.form.get('name'): use get if the key might not exist
  • request.form.getlist('name'): use getlist if the key is sent multiple times and you want a list of values. get only returns the first value.
2019/08/04
1391
8/4/2019 9:48:13 PM

To get the raw data, use request.data. This only works if it couldn't be parsed as form data, otherwise it will be empty and request.form will have the parsed data.

from flask import request
request.data
2019/08/04

For URL query parameters, use request.args.

search = request.args.get("search")
page = request.args.get("page")

For posted form input, use request.form.

email = request.form.get('email')
password = request.form.get('password')

For JSON posted with content type application/json, use request.get_json().

data = request.get_json()
2019/08/04

Here's an example of parsing posted JSON data and echoing it back.

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/foo', methods=['POST']) 
def foo():
    data = request.json
    return jsonify(data)

To post JSON with curl:

curl -i -H "Content-Type: application/json" -X POST -d '{"userId":"1", "username": "fizz bizz"}' http://localhost:5000/foo

Or to use Postman:

using postman to post JSON

2019/08/05

If you post JSON with content type application/json, use request.get_json() to get it in Flask. If the content type is not correct, None is returned. If the data is not JSON, an error is raised.

@app.route("/something", methods=["POST"])
def do_something():
    data = request.get_json()
2019/08/04

To get the raw post body regardless of the content type, use request.get_data(). If you use request.data, it calls request.get_data(parse_form_data=True), which will populate the request.form MultiDict and leave data empty.

2019/08/04