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