TypeError: catching classes that do not inherit from BaseException is not allowed

[SuryaSrikanthsml]

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Environment details

• OS:
• Python version: 3.7
• pip version:
• google-auth version: 2.6.3

Steps to reproduce

1. python Google app Engine standard environment, have google-auth in requirements.txt.
2. Occurs when an instance is terminated.

"Traceback (most recent call last):
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/google/auth/transport/requests.py", line 154, in del
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/requests/sessions.py", line 737, in close
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/requests/adapters.py", line 326, in close
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/urllib3/poolmanager.py", line 223, in clear
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/urllib3/_collections.py", line 100, in clear
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/urllib3/poolmanager.py", line 174, in
File "/layers/google.python.pip/pip/lib/python3.7/site-packages/urllib3/connectionpool.py", line 498, in close
TypeError: catching classes that do not inherit from BaseException is not allowed"

Unable to figure out if the error is in urllib3 or google-auth, was working fine with version 2.6.2

[arithmetic1728]

@lidizheng Could you take a look at it? It seems related to your #1007

[lidizheng]

Based on the exception message, this looks like an issue in CPython (similar to https://bugs.python.org/issue40097).

Step 1: The urllib3 trying to catch an exception named queue.Empty:

https://github.com/urllib3/urllib3/blob/e16beb210c03c6f5ce4e0908bddb6556442b6a37/src/urllib3/connectionpool.py#L506

Step 2: The built-in queue trying to determine if a faster (C extension) version of queue is available, if not it will use normal exception, hence no error; if there is a C extension, it will use that _queue.Empty:

https://github.com/python/cpython/blob/ac6c3de03c5bb06a9a463701fb297148f5a5746f/Lib/queue.py#L16

Step 3: The C extension building the exception, but didn't provide a base class:

https://github.com/python/cpython/blob/ac6c3de03c5bb06a9a463701fb297148f5a5746f/Modules/_queuemodule.c#L409

---

As a workaround, we can silence this exception, make it non-fatal.

[lidizheng]

Mitigation fix is posted at #1027, PTAL.

[arithmetic1728]

Fix is released in 2.6.6. Closing the issue.