Method _make_substitution

Lib/typing.py:1481–1541

Create a list of new type arguments.

(self, args, new_arg_by_param)

        return tuple(self._make_substitution(self.__args__, new_arg_by_param))

    def _make_substitution(self, args, new_arg_by_param):
        """Create a list of new type arguments."""
        new_args = []
        for old_arg in args:
            if isinstance(old_arg, type):
                new_args.append(old_arg)
                continue

            substfunc = getattr(old_arg, '__typing_subst__', None)
            if substfunc:
                new_arg = substfunc(new_arg_by_param[old_arg])
            else:
                subparams = getattr(old_arg, '__parameters__', ())
                if not subparams:
                    new_arg = old_arg
                else:
                    subargs = []
                    for x in subparams:
                        if isinstance(x, TypeVarTuple):
                            subargs.extend(new_arg_by_param[x])
                        else:
                            subargs.append(new_arg_by_param[x])
                    new_arg = old_arg[tuple(subargs)]

            if self.__origin__ == collections.abc.Callable and isinstance(new_arg, tuple):
                # Consider the following `Callable`.
                #   C = Callable[[int], str]
                # Here, `C.__args__` should be (int, str) - NOT ([int], str).
                # That means that if we had something like...
                #   P = ParamSpec('P')
                #   T = TypeVar('T')
                #   C = Callable[P, T]
                #   D = C[[int, str], float]
                # ...we need to be careful; `new_args` should end up as
                # `(int, str, float)` rather than `([int, str], float)`.
                new_args.extend(new_arg)
            elif _is_unpacked_typevartuple(old_arg):
                # Consider the following `_GenericAlias`, `B`:
                #   class A(Generic[*Ts]): ...
                #   B = A[T, *Ts]
                # If we then do:
                #   B[float, int, str]
                # The `new_arg` corresponding to `T` will be `float`, and the
                # `new_arg` corresponding to `*Ts` will be `(int, str)`. We
                # should join all these types together in a flat list
                # `(float, int, str)` - so again, we should `extend`.
                new_args.extend(new_arg)
            elif isinstance(old_arg, tuple):
                # Corner case:
                #    P = ParamSpec('P')
                #    T = TypeVar('T')
                #    class Base(Generic[P]): ...
                # Can be substituted like this:
                #    X = Base[[int, T]]
                # In this case, `old_arg` will be a tuple:
                new_args.append(
                    tuple(self._make_substitution(old_arg, new_arg_by_param)),
                )