Set a configuration entry

    :param key: key name
    :param value: value for this key
    :raises KeyError: if key is not str

def set_entry(key, value):
    """
    Set a configuration entry

    :param key: key name
    :param value: value for this key
    :raises KeyError: if key is not str
    """
    if type(key) != str:
        raise KeyError('key must be str')
    _config[key] = value