Python garbage collection

You haven't provided enough information - this depends on the specifics of the object you are creating and what else you're doing with it in the loop. If the object does not create circular references, it should be deallocated on the next iteration. For example, the code

for x in range(100000):
  obj = " " * 10000000

will not result in ever-increasing memory allocation.

This is an old error that was corrected for some types in python 2.5. What was happening was that python was not so good at collecting things like empty lists/dictionaries/tupes/floats/ints. In python 2.5 this was fixed...mostly. However floats and ints are singletons for comparisons so once one of those is created it stays around as long as the interpreter is alive. I've been bitten by this worst when dealing with large amount of floats since they have a nasty habit of being unique. This was characterized for python 2.4 and updated about it being folded into python 2.5

The best way I've found around it is to upgrade to python 2.5 or newer to take care of the lists/dictionaries/tuples issue. For numbers the only solution is to not let large amounts of numbers get into python. I've done it with my own wrapper to a c++ object, but I have the impression that numpy.array will give similar results.

As a post script I have no idea what has happened to this in python 3, but I'm suspicious that numbers are still part of a singleton. So the memory leak is actually a feature of the language.

If you're creating circular references, your objects won't be deallocated immediately, but have to wait for a GC cycle to run.

You could use the weakref module to address this problem, or explicitly del your objects after use.

I found that in my case (with Python 2.5.1), with circular references involving classes that have __del__() methods, not only was garbage collection not happening in a timely manner, the __del__() methods of my objects were never getting called, even when the script exited. So I used weakref to break the circular references and all was well.

Kudos to Miles who provided all the information in his comments for me to put this together.

Here's one thing you can do at the REPL to force a dereferencing of a variable:

>>> x = 5
>>> x
5
>>> del x
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined

weakref can be used for circular object structured code as in the explained example