Clearing data from the List ,Dictionary and Tuples

[psbasha]

Hi,

Is it mandatory to clear the data from the List ,Dictionary and Tuples after using it?.

- PSB

[bartonc]

Hi,

Is it mandatory to clear the data from the List ,Dictionary and Tuples after using it?.

- PSB

No. It is not.

[psbasha]

What are the effects of not clearing the list in terms of performance/memory consumption?

-PSB

[bartonc]

What are the effects of not clearing the list in terms of performance/memory consumption?

-PSB

from section 1.10 of Extending and Embedding in Python Manuals:

Since Python makes heavy use of malloc() and free(), it needs a strategy to avoid memory leaks as well as the use of freed memory. The chosen method is called reference counting. The principle is simple: every object contains a counter, which is incremented when a reference to the object is stored somewhere, and which is decremented when a reference to it is deleted. When the counter reaches zero, the last reference to the object has been deleted and the object is freed.

An alternative strategy is called automatic garbage collection. (Sometimes, reference counting is also referred to as a garbage collection strategy, hence my use of ``automatic'' to distinguish the two.) The big advantage of automatic garbage collection is that the user doesn't need to call free() explicitly. (Another claimed advantage is an improvement in speed or memory usage -- this is no hard fact however.) The disadvantage is that for C, there is no truly portable automatic garbage collector, while reference counting can be implemented portably (as long as the functions malloc() and free() are available -- which the C Standard guarantees). Maybe some day a sufficiently portable automatic garbage collector will be available for C. Until then, we'll have to live with reference counts.

While Python uses the traditional reference counting implementation, it also offers a cycle detector that works to detect reference cycles. This allows applications to not worry about creating direct or indirect circular references; these are the weakness of garbage collection implemented using only reference counting. Reference cycles consist of objects which contain (possibly indirect) references to themselves, so that each object in the cycle has a reference count which is non-zero. Typical reference counting implementations are not able to reclaim the memory belonging to any objects in a reference cycle, or referenced from the objects in the cycle, even though there are no further references to the cycle itself.

The cycle detector is able to detect garbage cycles and can reclaim them so long as there are no finalizers implemented in Python (__del__() methods). When there are such finalizers, the detector exposes the cycles through the gc module (specifically, the garbage variable in that module). The gc module also exposes a way to run the detector (the collect() function), as well as configuration interfaces and the ability to disable the detector at runtime. The cycle detector is considered an optional component; though it is included by default, it can be disabled at build time using the --without-cycle-gc option to the configure script on Unix platforms (including Mac OS X) or by removing the definition of WITH_CYCLE_GC in the pyconfig.h header on other platforms. If the cycle detector is disabled in this way, the gc module will not be available.