.. class:: AbstractContextManager
An :term:`abstract base class` for classes that implement
- :meth:`object.__enter__` and :meth:`object.__exit__`. A default
- implementation for :meth:`object.__enter__` is provided which returns
- ``self`` while :meth:`object.__exit__` is an abstract method which by default
+ :meth:`~object.__enter__` and :meth:`~object.__exit__`. A default
+ implementation for :meth:`~object.__enter__` is provided which returns
+ ``self`` while :meth:`~object.__exit__` is an abstract method which by default
returns ``None``. See also the definition of :ref:`typecontextmanager`.
.. versionadded:: 3.6
.. class:: AbstractAsyncContextManager
An :term:`abstract base class` for classes that implement
- :meth:`object.__aenter__` and :meth:`object.__aexit__`. A default
- implementation for :meth:`object.__aenter__` is provided which returns
- ``self`` while :meth:`object.__aexit__` is an abstract method which by default
+ :meth:`~object.__aenter__` and :meth:`~object.__aexit__`. A default
+ implementation for :meth:`~object.__aenter__` is provided which returns
+ ``self`` while :meth:`~object.__aexit__` is an abstract method which by default
returns ``None``. See also the definition of
:ref:`async-context-managers`.
.. function:: nullcontext(enter_result=None)
- Return a context manager that returns *enter_result* from ``__enter__``, but
+ Return a context manager that returns *enter_result* from :meth:`~object.__enter__`, but
otherwise does nothing. It is intended to be used as a stand-in for an
optional context manager, for example::
For example, the output of :func:`help` normally is sent to *sys.stdout*.
You can capture that output in a string by redirecting the output to an
:class:`io.StringIO` object. The replacement stream is returned from the
- ``__enter__`` method and so is available as the target of the
+ :meth:`~object.__enter__` method and so is available as the target of the
:keyword:`with` statement::
with redirect_stdout(io.StringIO()) as f:
A base class that enables a context manager to also be used as a decorator.
Context managers inheriting from ``ContextDecorator`` have to implement
- ``__enter__`` and ``__exit__`` as normal. ``__exit__`` retains its optional
+ :meth:`~object.__enter__` and :meth:`~object.__exit__` as normal.
+ ``__exit__`` retains its optional
exception handling even when used as a decorator.
``ContextDecorator`` is used by :func:`contextmanager`, so you get this
Catching exceptions from ``__enter__`` methods
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-It is occasionally desirable to catch exceptions from an ``__enter__``
+It is occasionally desirable to catch exceptions from an :meth:`~object.__enter__`
method implementation, *without* inadvertently catching exceptions from
-the :keyword:`with` statement body or the context manager's ``__exit__``
+the :keyword:`with` statement body or the context manager's :meth:`~object.__exit__`
method. By using :class:`ExitStack` the steps in the context management
protocol can be separated slightly in order to allow this::