def unpatch(*module_names):
    """undo :func:`patch`\es to standard library modules

    this function takes one or more module names and puts back their patched
    attributes to the standard library originals.

    valid arguments are the same as for :func:`patch`.

    with no arguments, undoes all monkeypatches that have been applied

    :raises: ``ValueError`` if an unknown module name is provided
    """
    if not module_names:
        module_names = _standard.keys()

    log.info("undoing monkey-patches in-place (%d modules)" %
             len(module_names))

    for module_name in module_names:
        if module_name not in _standard:
            raise ValueError("'%s' is not greenhouse-patchable" % module_name)

    for module_name in module_names:
        module = __import__(module_name, {}, {}, module_name.rsplit(".", 1)[0])
        for attr, value in _standard[module_name].items():
            setattr(module, attr, value)