Issue2660

See https://github.com/pypa/pip/issues/5121 for environment, console session and a stack dump. Briefly:

# Upgrade to 9.0.3
[root@b5718b55e70d /]# jython -m pip install --upgrade pip
Collecting pip
  Downloading pip-9.0.3-py2.py3-none-any.whl (1.4MB)
    100% |████████████████████████████████| 1.4MB 379kB/s 
Installing collected packages: pip
  Found existing installation: pip 9.0.1
    Uninstalling pip-9.0.1:
      Successfully uninstalled pip-9.0.1
Successfully installed pip-9.0.3

# Install pytest
[root@b5718b55e70d /]# jython -m pip install pytest
Collecting pytest
Exception:
Traceback (most recent call last):
  File "/usr/share/jython/Lib/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
...
  File "/usr/share/jython/Lib/site-packages/pip/_vendor/urllib3/util/selectors.py", line 344, in register
    key = super(PollSelector, self).register(fileobj, events, data)
  File "/usr/share/jython/Lib/site-packages/pip/_vendor/urllib3/util/selectors.py", line 197, in register
    key = SelectorKey(fileobj, self._fileobj_lookup(fileobj), events, data)
  File "/usr/share/jython/Lib/site-packages/pip/_vendor/urllib3/util/selectors.py", line 181, in _fileobj_lookup
    return _fileobj_to_fd(fileobj)
  File "/usr/share/jython/Lib/site-packages/pip/_vendor/urllib3/util/selectors.py", line 50, in _fileobj_to_fd
    raise ValueError("Invalid file object: {0!r}".format(fileobj))
ValueError: Invalid file object: <ssl.SSLSocket object at 0x1a4>

It would be nice if we had a minimal code snippet that reproduced this issue solely involving urllib3, i.e. independently from pip.

I cannot reproduce this problem with requests which uses urllib3. However, I can reproduce original issue with pip 9.0.3.