The gc module is only available if the interpreter was built
with the optional cyclic garbage detector (enabled by default). If
this was not enabled, an ImportError is raised by attempts
to import this module.
This module provides an interface to the optional garbage collector. It
provides the ability to disable the collector, tune the collection
frequency, and set debugging options. It also provides access to
unreachable objects that the collector found but cannot free. Since the
collector supplements the reference counting already used in Python, you
can disable the collector if you are sure your program does not create
reference cycles. Automatic collection can be disabled by calling
gc.disable(). To debug a leaking program call
gc.set_debug(gc.DEBUG_LEAK).
Set the garbage collection debugging flags.
Debugging information will be written to sys.stderr. See below
for a list of debugging flags which can be combined using bit
operations to control debugging.
Set the garbage collection thresholds (the collection frequency).
Setting threshold0 to zero disables collection.
The GC classifies objects into three generations depending on how many
collection sweeps they have survived. New objects are placed in the
youngest generation (generation 0). If an object survives a
collection it is moved into the next older generation. Since
generation 2 is the oldest generation, objects in that
generation remain there after a collection. In order to decide when
to run, the collector keeps track of the number object allocations and
deallocations since the last collection. When the number of
allocations minus the number of deallocations exceeds
threshold0, collection starts. Initially only generation
0 is examined. If generation 0 has been examined more
than threshold1 times since generation 1 has been
examined, then generation 1 is examined as well. Similarly,
threshold2 controls the number of collections of generation
1 before collecting generation 2.
A list of objects which the collector found to be unreachable
but could not be freed (uncollectable objects). Objects that have
__del__() methods and create part of a reference cycle cause
the entire reference cycle to be uncollectable. If
DEBUG_SAVEALL is set, then all unreachable objects will
be added to this list rather than freed.
The following constants are provided for use with
set_debug():
Print information of uncollectable objects found (objects which are
not reachable but cannot be freed by the collector). These objects
will be added to the garbage list.
The debugging flags necessary for the collector to print
information about a leaking program (equal to DEBUG_COLLECTABLE |
DEBUG_UNCOLLECTABLE | DEBUG_INSTANCES | DEBUG_OBJECTS | DEBUG_SAVEALL).