def _split(string, sep):
    """
    Utility function to split a string by a given separation character or str

    :type string: str
    :param string: string to split
    :type sep: str
    :param sep: substring to split by
    """
    n = string.find(sep)
    if n >= 0:
        return string[:n], string[n + len(sep):]
    else:
        return string, ''