How to use the handprint.credentials.credentials_files.credentials_filename function in handprint

def save_credentials(self, service, supplied_file):
        if not path.isdir(Credentials.creds_dir):
            if __debug__: log('creating credentials dir: {}.', Credentials.creds_dir)
            make_dir(Credentials.creds_dir)
        dest_file = path.join(Credentials.creds_dir, credentials_filename(service))
        copy_file(supplied_file, dest_file)

def __init__(self):
        cfile = path.join(self.credentials_dir(), credentials_filename('google'))
        if __debug__: log('credentials file for google is {}', cfile)
        if not path.exists(cfile):
            raise AuthFailure('Credentials for Google have not been installed')
        elif not readable(cfile):
            raise AuthFailure('Google credentials file unreadable: {}'.format(cfile))

        # Haven't been able to make it work; only the environment variable
        # approach has been working for me.
        #
        # with open(self.credentials_file, 'r') as file:
        #     self.credentials = json.load(file)
        os.environ['GOOGLE_APPLICATION_CREDENTIALS'] = cfile

def __init__(self):
        cfile = path.join(self.credentials_dir(), credentials_filename('amazon'))
        if __debug__: log('credentials file for amazon is {}', cfile)
        if not path.exists(cfile):
            raise AuthFailure('Credentials for Amazon have not been installed')
        elif not readable(cfile):
            raise AuthFailure('Amazon credentials file unreadable: {}'.format(cfile))

        try:
            with open(cfile, 'r') as file:
                self.credentials = json.load(file)
        except Exception as ex:
            raise AuthFailure(
                'Unable to parse Amazon exceptions file: {}'.format(str(ex)))

def __init__(self):
        cfile = path.join(self.credentials_dir(), credentials_filename('microsoft'))
        if __debug__: log('credentials file for microsoft is {}', cfile)
        if not path.exists(cfile):
            raise AuthFailure('Credentials for Microsoft have not been installed')
        elif not readable(cfile):
            raise AuthFailure('Microsoft credentials file unreadable: {}'.format(cfile))

        try:
            with open(cfile, 'r') as file:
                creds = json.load(file)
                self.credentials = creds['subscription_key']
        except Exception as ex:
            raise AuthFailure(
                'Unable to parse Microsoft exceptions file: {}'.format(str(ex)))