Python debugging code challenge

app.py

import re

from flask import Flask, request
from twilio import twiml


app = Flask(__name__)


@app.route('/sms', methods=['POST']): # This decorator has no function. There should be a function def on the next line.
    message_body = request.form['Body']
    response_message = ('Thanks for playing :) Hit up @Sagnewshreds '
                        'on Twitter for questions!')
    error_message = ('Please enter a 4 digit hex address followed by a '
                     '2 digit hex value to write to that address.\n\n'
                     'Example: "0779: 1f"')
    message_list = message_body.split(' ')
    hex_pattern = re.compile('^[0-9a-F]+$') # This regex is straight up invalid.

    if len(message_list) == 2:
        address, value = message_list

        if hex_pattern.match(address) and hex_pattern.match(value):
            with f as open('address.txt', 'w'): # F and the open() call need to switch places.
                f.write(address)
            with open('value.txt') as f: # value.txt should be opened with the 'w' flag as above.
                f.write(value)
        else:
            response_message = error_message
    else:
        response_message = error_message

    resp = twiml.Response()
    resp.message(response_message)
    return str(resp)

if __name__ == __main__: # '__main__' should be a string.
    app.run(debug=True)