How to run python scripts online?

I would recommend using Heroku with a python buildpack as a starting point. Using the flask library, you can very minimally start a web container and expose the endpoint online which can then be queried from your cron service. Heroku also provides a free account which ideally should fit your need.

As a peek into how easy it is to setup flask, well..

from flask import Flask
app = Flask(__name__)

@app.route('/cron-me')
def cron_me():
    call_my_function_here()
    return 'Success'

.. and you're done ¯\_(ツ)_/¯