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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def import_app_credentials(filename=CREDENTIALS_FILENAME):
 """Import app credentials from configuration file. Parameters filename (str) Name of configuration file. Returns credentials (dict) All your app credentials and information imported from the configuration file. """

    with open(filename, 'r') as config_file:
        config = safe_load(config_file)

    client_id = config['client_id']
    client_secret = config['client_secret']
    redirect_url = config['redirect_url']

    config_values = [client_id, client_secret, redirect_url]

    for value in config_values:
        if value in DEFAULT_CONFIG_VALUES:
            exit('Missing credentials in {}'.format(filename))

    credentials = {
        'client_id': client_id,
        'client_secret': client_secret,
        'redirect_url': redirect_url,
        'scopes': set(config['scopes']),
    }

    return credentials