Stack frames and generators¶
Let’s define a custom class
>>> class Canary(object): ... pass
Suppose we’ve a generator that uses it
>>> def count_to_three(): ... tweety = Canary() ... yield 1 ... yield 2 ... yield 3
and we make it active
>>> it = count_to_three() >>> next(it) 1
Now we can see that our Canary object is alive in memory
>>> import objgraph >>> objgraph.count('Canary') 1
and we can see what holds it in memory
>>> objgraph.show_backrefs(objgraph.by_type('Canary'), ... max_depth=7, ... filename='canary.png') Graph written to ....dot (15 nodes) Image generated as canary.png
Or we can examine just one of the reference chains leading straight to a module.
>>> objgraph.show_chain( ... objgraph.find_backref_chain(objgraph.by_type('Canary'), ... objgraph.is_proper_module), ... filename='canary-chain.png') Graph written to ....dot (11 nodes) Image generated as canary-chain.png
To a first approximation, modules are garbage-collection roots, which makes the latter technique most useful.