I'm trying to write a context manager to handle database connections, under the
principle that I should not rely on CPython's reference-counting semantics to
clean up scarce resources, like connections.
I wrote:
@contexlib.contextmanager
def ensure_connection(con=None):
con_created = False
if con is None:
con_created, con = True, make_connection()
try:
yield con
finally:
if con_created:
con.close()
However, then I read the following paragraph from PEP-343:
Note that we're not guaranteeing that the finally-clause is
executed immediately after the generator object becomes unused,
even though this is how it will work in CPython. This is similar
to auto-closing files: while a reference-counting implementation
like CPython deallocates an object as soon as the last reference
to it goes away, implementations that use other GC algorithms do
not make the same guarantee. This applies to Jython, IronPython,
and probably to Python running on Parrot.
That suggests that I cannot rely on the contextlib.contextmanager decorator to
ensure that the connection is closed and would have to write my own object with
__enter__ and __exit__ methods to guarantee this.
Is this understanding accurate? If so, could someone illustrate why this is
so?
Thanks,
Johann
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