Function _paramspec_prepare_subst

Lib/typing.py:1144–1158

(self, alias, args)

def _paramspec_prepare_subst(self, alias, args):
    params = alias.__parameters__
    i = params.index(self)
    if i == len(args) and self.has_default():
        args = (*args, self.__default__)
    if i >= len(args):
        raise TypeError(f"Too few arguments for {alias}")
    # Special case where Z[[int, str, bool]] == Z[int, str, bool] in PEP 612.
    if len(params) == 1 and not _is_param_expr(args[0]):
        assert i == 0
        args = (args,)
    # Convert lists to tuples to help other libraries cache the results.
    elif isinstance(args[i], list):
        args = (*args[:i], tuple(args[i]), *args[i+1:])
    return args


@_tp_cache