https://github.com/python/cpython/commit/d00a9e0176e9a1e2dd213a137757da36e07... commit: d00a9e0176e9a1e2dd213a137757da36e071bd81 branch: 3.11 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: miss-islington <31488909+miss-islington@users.noreply.github.com> date: 2022-08-30T08:06:19-07:00 summary: gh-95337: update TypeVarTuple example (GH-95338) Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com> (cherry picked from commit 07f12b5c1567581aa77d523e462b0e7f75c1f05c) Co-authored-by: Adrian Garcia Badaracco <1755071+adriangb@users.noreply.github.com> files: M Doc/library/typing.rst diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst index 0951916f080..76394066431 100644 --- a/Doc/library/typing.rst +++ b/Doc/library/typing.rst @@ -1305,20 +1305,25 @@ These are not used in annotations. They are building blocks for creating generic T = TypeVar('T') Ts = TypeVarTuple('Ts') - def remove_first_element(tup: tuple[T, *Ts]) -> tuple[*Ts]: - return tup[1:] + def move_first_element_to_last(tup: tuple[T, *Ts]) -> tuple[*Ts, T]: + return (*tup[1:], tup[0]) # T is bound to int, Ts is bound to () - # Return value is (), which has type tuple[()] - remove_first_element(tup=(1,)) + # Return value is (1,), which has type tuple[int] + move_first_element_to_last(tup=(1,)) # T is bound to int, Ts is bound to (str,) - # Return value is ('spam',), which has type tuple[str] - remove_first_element(tup=(1, 'spam')) + # Return value is ('spam', 1), which has type tuple[str, int] + move_first_element_to_last(tup=(1, 'spam')) # T is bound to int, Ts is bound to (str, float) - # Return value is ('spam', 3.0), which has type tuple[str, float] - remove_first_element(tup=(1, 'spam', 3.0)) + # Return value is ('spam', 3.0, 1), which has type tuple[str, float, int] + move_first_element_to_last(tup=(1, 'spam', 3.0)) + + # This fails to type check (and fails at runtime) + # because tuple[()] is not compatible with tuple[T, *Ts] + # (at least one element is required) + move_first_element_to_last(tup=()) Note the use of the unpacking operator ``*`` in ``tuple[T, *Ts]``. Conceptually, you can think of ``Ts`` as a tuple of type variables