def replace(scope, strings, source, dest):
    """
    Returns a copy of the given string (or list of strings) in which all
    occurrences of the given source are replaced by the given dest.

    :type  strings: string
    :param strings: A string, or a list of strings.
    :type  source: string
    :param source: What to replace.
    :type  dest: string
    :param dest: What to replace it with.
    :rtype:  string
    :return: The resulting string, or list of strings.
    """
    return [s.replace(source[0], dest[0]) for s in strings]