Maximum recursion depth exceeded while pickling an object

[tjlaboss]

Bug Description

Pickling an MCNP_Problem results in a RecursionError.

To Reproduce

>>> deck = montepy.read_input("my_input.imcnp")
>>> with open('deck_112.pkl', 'wb') as f:
>>>     pickle.dump(deck, f)

Error Message

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
RecursionError: maximum recursion depth exceeded while pickling an object

MCNP input file snippet

I will work on producing a Minimal Reproducible Example. In the meanwhile, I can share the model that caused this internally.

Version

• Version 1.1.2. Rolling back to 1.1.1 solved the issue.

[MicahGale]

Once we can figure out what input type that broke this we'll need to add it to the test suite.

[tjlaboss]

I have confirmed that it is some sort of tally.

[MicahGale]

I had my hunches, but I was hoping it wasn't.

[tjlaboss]

PEBKAC: I was accidentally using an unsupported Python version, 3.9. It worked fine in 3.13.

Nevertheless a very strange bug: it only arose for tallies with >191 tally multiplier bins.

Edit: Never mind, I was right! Python 3.9 is still officially supported in develop and will be removed in minor-rel-dev.

[MicahGale]

What version of python?

[MicahGale]

As we discussed 3.9 is still supported for MontePy 1.1. Also I'm still troubled by this popping up sometimes. I wonder if 3.13 conversion just delayed the issue's severity and didn't eliminate it. Could you still create a MWE for this? I think sys._setrecursionlimit(50) or something similar will help a lot in minimizing MWE size.

[tjlaboss]

The challenge is the M in the example, because any recursion limit low enough to trigger the issue causes import issues. I wonder if I can lower the recursion limit after imports and loading but before pickling.

I was able to reproduce on very large inputs by toying with the recursion limit. The default is 1000.

Configurations:

1. Old Python, Old MontePy

• Python 3.9
• NumPy 1.22
• MontePy 1.0 <= 1.1.1
• Result: No problems at standard recursion limit. Reproducible lowering it to 100.

2. Old Python, New MontePy

• Python 3.9
• NumPy 1.22
• MontePy >= 1.1.2
• Result: Original issue. Solved by raising recursion limit to 10,000

3. New Python, Old MontePy

• Python 3.14
• NumPy 2.0
• MontePy 1.0 <= 1.1.1
• Result: No problems at standard recursion limit. Was not reproducible lowering it to 100 and still do imports.

4. New Python, New MontePy

• Python 3.14
• NumPy 2.0
• MontePy >= 1.1.2
• Result: No problems at standard recursion limit. Reproducible lowering it to 100.

Therefore, it seems reasonable to conclude that something within (Python between 3.9-3.14) or (NumPy between 1.22 and 2.0) changed that is triggered by something within (MontePy between 1.1.1 and 1.1.2) that changed.

[MicahGale]

Would you be willing to try New Python, old numpy, new MontePy?

[tjlaboss]

No. The last NumPy 1 release (1.26) only supports up through Python 3.12.