mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-09-30 12:21:51 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 9

bpo-31564: Update typing documentation (GH-3696) (GH-3715)

Browse source 
Mention that ``NewType`` can derive from another ``NewType``.
(cherry picked from commit 039b25d8fd)
This commit is contained in:
Miss Islington (bot) 2017-09-23 19:46:24 -07:00 • committed by Mariatta
parent 7e32cee1a6
commit 018e6b9f69
1 changed files with 9 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

12
Doc/library/typing.rst
View file

@ -111,8 +111,7 @@ More precisely, the expression ``some_value is Derived(some_value)`` is always
true at runtime. true at runtime.
This also means that it is not possible to create a subtype of ``Derived`` This also means that it is not possible to create a subtype of ``Derived``
since it is an identity function at runtime, not an actual type. Similarly, it since it is an identity function at runtime, not an actual type::
is not possible to create another :func:`NewType` based on a ``Derived`` type::
from typing import NewType from typing import NewType
@ -121,9 +120,16 @@ is not possible to create another :func:`NewType` based on a ``Derived`` type::
# Fails at runtime and does not typecheck # Fails at runtime and does not typecheck
class AdminUserId(UserId): pass class AdminUserId(UserId): pass
# Also does not typecheck However, it is possible to create a :func:`NewType` based on a 'derived' ``NewType``::
from typing import NewType
UserId = NewType('UserId', int)
ProUserId = NewType('ProUserId', UserId) ProUserId = NewType('ProUserId', UserId)
and typechecking for ``ProUserId`` will work as expected.
See :pep:`484` for more details. See :pep:`484` for more details.
.. note:: .. note::