Checks if arg is list-like. This excludes strings and dicts.

def _is_list(arg):
    """Checks if arg is list-like. This excludes strings and dicts."""
    if isinstance(arg, dict):
        return False
    if isinstance(arg, str): # Python 3-only, as str has __iter__
        return False
    return (not _has_method(arg, "strip")
            and _has_method(arg, "__getitem__")
            or _has_method(arg, "__iter__"))