diagnosing memory leak in python

Question

I've been trying to debug a memory leak in the Coopr package using objgraph: https://gist.github.com/3855150

I have it pinned down to a _SetContainer object, but can't seem to figure out why that object is persisting in memory. Here's the result of objgraph.show_refs:

How do I go about finding the circular reference and how can I get the the garbage collector to collect the _SetContainer instance?

I previously thought that the class itself might have a self-reference (the tuple just below the class on the right in the image above). But objgraph always shows inherited classes always as having a self-referencing tuple. You can see a very simple test case here.

Answer 1

It's mostly guessing from the output of objgraph, but it seems that the instance is in a cycle and its class has a __del__. In this situation, the object is kept alive forever in CPython. Check it with:

import gc; gc.collect(); print gc.garbage

http://docs.python.org/library/gc.html#gc.garbage