def get_callable_handler_function(src, handler):
    """Translate a string of the form "module.function" into a callable
    function.

    :param str src:
      The path to your Lambda project containing a valid handler file.
    :param str handler:
      A dot delimited string representing the `<module>.<function name>`.
    """

    # "cd" into `src` directory.
    os.chdir(src)

    module_name, function_name = handler.split(".")
    filename = get_handler_filename(handler)

    path_to_module_file = os.path.join(src, filename)
    module = load_source(module_name, path_to_module_file)
    return getattr(module, function_name)