def get_value_format(value_format=str):
    """Create a formatting function from a generic value_format argument.
    
    Parameters
    ----------
    value_format : str or Callable

    Returns
    -------
    Callable
    """
    if value_format is None:
        value_format = ""
    if isinstance(value_format, str):
        format_str = "{0:" + value_format + "}"
        value_format = lambda x: format_str.format(x)
    
    return value_format