bpo-33468: Add try-finally contextlib.contextmanager example (GH-7816) (GH-8425)
(cherry picked from commit bde782bb594edffeabe978abeee2b7082ab9bc2a)
Co-authored-by: Matthias Bussonnier <bussonniermatthias@gmail.com>
diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
index 0b1f4f7..793bd63 100644
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -47,22 +47,28 @@
function for :keyword:`with` statement context managers, without needing to
create a class or separate :meth:`__enter__` and :meth:`__exit__` methods.
- A simple example (this is not recommended as a real way of generating HTML!)::
+ While many objects natively support use in with statements, sometimes a
+ resource needs to be managed that isn't a context manager in its own right,
+ and doesn't implement a ``close()`` method for use with ``contextlib.closing``
+
+ An abstract example would be the following to ensure correct resource
+ management::
from contextlib import contextmanager
@contextmanager
- def tag(name):
- print("<%s>" % name)
- yield
- print("</%s>" % name)
+ def managed_resource(*args, **kwds):
+ # Code to acquire resource, e.g.:
+ resource = acquire_resource(*args, **kwds)
+ try:
+ yield resource
+ finally:
+ # Code to release resource, e.g.:
+ release_resource(resource)
- >>> with tag("h1"):
- ... print("foo")
- ...
- <h1>
- foo
- </h1>
+ >>> with managed_resource(timeout=3600) as resource:
+ ... # Resource is released at the end of this block,
+ ... # even if code in the block raises an exception
The function being decorated must return a :term:`generator`-iterator when
called. This iterator must yield exactly one value, which will be bound to