Freeing memory from Python lists!

Chad Everett chat at
Wed Jul 11 17:48:50 EDT 2001

On 11 Jul 2001 14:53:06 -0500, Chris Spencer <clspence at> wrote:
>	I can confirm these results.  Why would a deleted list retain 90% of its
>memory usage after being deleted?  Sounds like a pointer is getting lost
>On 11 Jul 2001 11:41:25 -0700, msimpson at (Mike Simpson) wrote:
>>I can't figure out how to free the memory used in the creation of a
>>large list in Python.
>>I am running the Python 2.1 interpreter on Windows 2000 Professional
>>to run the following piece of code:
>>result = []
>>for count in xrange(510*478):
>>	result.append(count)
>>del result
>>By using Windows Task Manager I was able to determine that 4332K of
>>memory was used up until the end of the for loop, but only 960K of
>>memory was returned to the system after the call to "del".  Is there
>>any way to return the other 3372K of memory to the system without
>>quitting the Python interpreter?

Nothing has been lost.  As other responses have pointed out, you are seeing
a manifestation of the OS memory management algorithms.  To show you that
nothing has been "lost" do the following:

1. run python and get a python prompt

2. look at your memory allocation

3. do your:

result = []
for count in xrange(510*478):

4. look at memory usage

5. delete the result list

del result

6. look at memory usage

7. now build the list again

result = []
for count in xrange(510*478):

8. look at memory usage and you'll see it has only gone back up to the same 
   amount of memory at step 4.

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