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| -rw-r--r-- | Doc/library/typing.rst | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst index 1e48fec..bd04f73 100644 --- a/Doc/library/typing.rst +++ b/Doc/library/typing.rst @@ -111,8 +111,7 @@ More precisely, the expression ``some_value is Derived(some_value)`` is always true at runtime. 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 -is not possible to create another :func:`NewType` based on a ``Derived`` type:: +since it is an identity function at runtime, not an actual type:: 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 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) +and typechecking for ``ProUserId`` will work as expected. + See :pep:`484` for more details. .. note:: |