[FIXED] How do you list all warning filters in Python?

Issue

I just spent the day trying to remove this warning from my output:

sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name='/dev/null' mode='w' encoding='UTF-8'>

I just finished a binary search of about 100k lines of code to try to figure this out. I still haven't found what's leaving /dev/null open, but I did find that some of our code says:

warnings.simplefilter("always")

Removing that removes the warning. Hooray! I plan to remove that bit of code, but I'm curious of two things:

1. Could I have avoided doing a binary search for this somehow? Enabling TRACEMALLOC=1 was entirely ineffective (maybe because this is in third-party code we import?)

2. Once I remove this, is there a way to list all of the warning filters that are applied at a particular point in the code? Seems like an important thing to be able to analyze, but I can't figure out how.

Solution

Just grep for import warnings (or the from variant). It's not as though that's a common thing to import.

After executing someone else's code, you can always

warnings.simplefilter("ignore")

to disable what they enabled, even without reviewing their source code.

---

You can view current filters in this way:

>>> import warnings
>>> import pprint
>>> pprint.pprint(warnings.filters)
[('default', None, <class 'DeprecationWarning'>, '__main__', 0),
 ('ignore', None, <class 'DeprecationWarning'>, None, 0),
 ('ignore', None, <class 'PendingDeprecationWarning'>, None, 0),
 ('ignore', None, <class 'ImportWarning'>, None, 0),
 ('ignore', None, <class 'ResourceWarning'>, None, 0)]

Answered By - J_H

Answer Checked By - Dawn Plyler (PHPFixing Volunteer)