"TypeError": 'list' object is not callable flask

The problem is that your endpoint is returning a list. Flask only likes certain return types. The two that are probably the most common are

• a Response object
• a str (along with unicode in Python 2.x)

You can also return any callable, such as a function.

If you want to return a list of devices you have a couple of options. You can return the list as a string

@server.route('/devices')
def status():
    return ','.join(app.statusOfDevices())

or you if you want to be able to treat each device as a separate value, you can return a JSON response

from flask.json import jsonify

@server.route('/devices')
def status():
    return jsonify({'devices': app.statusOfDevices()})
    # an alternative with a complete Response object
    # return flask.Response(jsonify({'devices': app.statusOfDevices()}), mimetype='application/json')