CPython currently uses a reference-counting scheme with (optional)
delayed detection of cyclically linked garbage, which collects most
objects as soon as they become unreachable, but is not guaranteed to
collect garbage containing circular references.

Some objects contain references to "external" resources such as open
files. It is understood that these resources are freed when the object
is garbage-collected, but since garbage collection is not guaranteed to
happen, such objects also provide an explicit way to release the
external resource, usually a close() method.

Programs are strongly recommended to explicitly close such objects.

Reference: https://docs.python.org/3.6/reference/datamodel.htmlSigned-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>