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Apr 16, 2025
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typing docs: Clarify Protocol / runtime_checkable docs #132606

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typing docs: Clarify Protocol / runtime_checkable docs
JelleZijlstra Apr 16, 2025
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Update Doc/library/typing.rst
JelleZijlstra Apr 16, 2025
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8 changes: 5 additions & 3 deletions Doc/library/typing.rst
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Expand Up @@ -2455,7 +2455,8 @@ types.
See :pep:`544` for more details. Protocol classes decorated with
:func:`runtime_checkable` (described later) act as simple-minded runtime
protocols that check only the presence of given attributes, ignoring their
type signatures.
type signatures. Protocol classes without this decorator cannot be used
with :func:`isinstance` and :func:`issubclass`.

Protocol classes can be generic, for example::

Expand All @@ -2479,8 +2480,7 @@ types.
Mark a protocol class as a runtime protocol.

Such a protocol can be used with :func:`isinstance` and :func:`issubclass`.
This raises :exc:`TypeError` when applied to a non-protocol class. This
allows a simple-minded structural check, very similar to "one trick ponies"
This allows a simple-minded structural check, very similar to "one trick ponies"
in :mod:`collections.abc` such as :class:`~collections.abc.Iterable`. For example::

@runtime_checkable
Expand All @@ -2496,6 +2496,8 @@ types.
import threading
assert isinstance(threading.Thread(name='Bob'), Named)

This decorator raises :exc:`TypeError` when applied to a non-protocol class.

.. note::

:func:`!runtime_checkable` will check only the presence of the required
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