SimpleLazyObject raises RuntimeError if __class__ accessed while tracing execution

[rouyrre+django@…]

I found the issue while trying to profile a django application with pycallgraph. The issue is referenced there: ​https://github.com/gak/pycallgraph/issues/92

The issue is reproduced with the following code:

import sys
from django.utils.functional import SimpleLazyObject

def tracer(frame, event, arg):
    frame.f_locals['self'].__class__

sys.settrace(tracer)
SimpleLazyObject(lambda x: x)
sys.settrace(None)

I wrote a failing test in tests/regressiontests/utils/functional.py. The issue is solved by defining _wrapped=None in the LazyObject class in django/utils/functional.py and this does not seems to break anything, all tests still pass.

Do you prefer one commit for test + fix as it's a small issue or separate commits? Is the test written in the right place?

I can make a pull request once this ticket is created (as the commit guidelines specify I need a ticket number in the first place to commit & reference my code). Thanks for any comment about the issue or how to proceed.

[anonymous]

I commited the code there: ​https://github.com/blaze33/django/commit/772f4b0f357b34abd1041d99b990f4f5b88bed6e

[Russell Keith-Magee]

One commit for test + fix is fine.

[anonymous]

Code was updated as discussed with @spookylukey
​https://github.com/blaze33/django/commit/2f6d887bd0a110e3a662ac1d056d6cdabf38632b

[Aymeric Augustin]

The test should:

• either restore the existing trace function if there is one rather than disable it,
• or not run at all when a trace functions is active.

Otherwise this looks good.

[Aymeric Augustin <aymeric.augustin@…>]

In 9dc5702932a0031bc4fb5473f2cdccffc61dbe30:

Fixed #19456 -- Avoid infinite recursion when tracing LazyObject.init.

Thanks blaze33 for the patch.

[anonymous]

Good catch about restoring the trace function!
Thanks for the merge.