Stop hiding errors that occur inside __del__ methods

[jdufresne]

If an exception occurs inside the __del__ method, it should be reported to the developer. Not doing so could hide bugs.

Python automatically handles exceptions inside __del__ methods, for example:

class A:
    def __del__(self):
        1 / 0

A()
print("after del")

Results in the output:

$ python3 ~/blah.py
Exception ignored in: <function A.__del__ at 0x7fbbf2bbfc20>
Traceback (most recent call last):
  File "/home/jon/test.py", line 3, in __del__
    1 / 0
ZeroDivisionError: division by zero
after del

From this example, we can see the bug was not hidden and the code after __del__ still executed.

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Does travis tests pass with this change (enable it first in your forked repo and wait for the travis build to finish)?
• Is the new or changed code fully tested?
• [ ] Is a documentation update included (if this change modifies existing APIs, or introduces new ones)? N/A

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

[codecov-io]

Codecov Report

Merging #1281 into master will increase coverage by 0.13%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1281      +/-   ##
==========================================
+ Coverage   92.45%   92.59%   +0.13%     
==========================================
  Files          19       19              
  Lines        6415     6400      -15     
==========================================
- Hits         5931     5926       -5     
+ Misses        484      474      -10

Impacted Files	Coverage Δ
redis/connection.py	81.28% <100%> (+0.57%)	⬆️
redis/client.py	85.97% <100%> (+0.17%)	⬆️
redis/utils.py	68.75% <0%> (ø)	⬆️
tests/test_multiprocessing.py	78.78% <0%> (ø)	⬆️
tests/test_encoding.py	96% <0%> (ø)	⬆️
tests/test_connection_pool.py	97.84% <0%> (ø)	⬆️
tests/test_pubsub.py	99.15% <0%> (ø)	⬆️
tests/test_sentinel.py	99.14% <0%> (ø)	⬆️
... and 6 more

---

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[andymccurdy]

I too do not like hiding these errors. I'm going to merge this but I'm concerned about what corner cases might be exposed in real world code that the test suite doesn't adequately cover. If the next release causes significant issues for folks I may end up reversing this.

[jdufresne]

I understand, thanks. The only potential side effect should be output on stderr, no breakage or change in functionality. If you do decide to revert it, can you please CC me and I'll see if I can address it more directly?

[andymccurdy]

Sure, sounds good. Thanks!