import six.moves.http_client locks interpreter

[pelson]

When importing six.moves.http_client within a script my interpreter freezes up. I don't get the same behaviour when importing in the REPL:

$ python       
Python 3.6.6 |Anaconda, Inc.| (default, Jun 28 2018, 17:14:51) 
[GCC 7.2.0] on linux
...
>>> import six.moves.http_client
>>> 

$ cat foo.py
import six
print('Six version: ', six.__version__)
import six.moves.http_client
print('six.moves.http_client')

$ python foo.py
Six version:  1.11.0
...
<wait a very long time and then KeyboardInterrupt to get some traceback>
...
^CTraceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 888, in _find_spec
AttributeError: '_SixMetaPathImporter' object has no attribute 'find_spec'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "foo.sh", line 3, in <module>
    import six.moves.http_client
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 951, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 890, in _find_spec
  File "<frozen importlib._bootstrap>", line 867, in _find_spec_legacy
  File "<frozen importlib._bootstrap>", line 449, in spec_from_loader
  File "lib/python3.6/site-packages/six.py", line 216, in is_package
    return hasattr(self.__get_module(fullname), "__path__")
  File "lib/python3.6/site-packages/six.py", line 118, in __getattr__
    _module = self._resolve()
  File "lib/python3.6/site-packages/six.py", line 115, in _resolve
    return _import_module(self.mod)
  File "lib/python3.6/site-packages/six.py", line 82, in _import_module
    __import__(name)
  File "<frozen importlib._bootstrap>", line 202, in _lock_unlock_module
  File "<frozen importlib._bootstrap>", line 98, in acquire
KeyboardInterrupt

Changing the import to from six.moves import http_client results in the import working fine. I'm on a RHEL6 machine, but using the Anaconda distribution (hence the modern GCC compiler). I tried the same on my mac and couldn't reproduce the issue.

This might seem esoteric, but I've traced this back from urllib3 which itself I traced from requests. The line that makes this import call is in urllibr3.exceptions. I'll submit a PR against urllib3 for this, but wanted to raise this here - I guess it is not expected behaviour, and worth sharing.