def simple_template_render(template, output, var_dict):
    """
    render template file to output file
    with variable substitution defined by var_dict.
    template file vars are defined within {var}.

    :param template: str. Absolute file name for template file.
    :param output: str. Absolute file name for output file (create or overwrite).
    :param var_dict: Dict[str, str].
    :return: None.
    """
    with open(template, 'r') as f:
        l = f.read()
    nl = l.format(**var_dict)
    with open(output, 'w') as f:
        f.writelines([nl])
