You can access the form data submitted via a POST or PUT request in Flask via the request.form attribute.
from flask import Flask, request
app = Flask(import_name=__name__)
@app.route("/echo", methods=["POST"])
def echo():
name = request.form.get("name", "")
age = request.form.get("age", "")
response = "Hey there {}! You said you are {} years old.".format(name, age)
return response
app.run()