title: Pip six.add_metaclass error
body: <p>A few days ago I started getting the following error when using pip (1,2 or 3) to install. </p>
  
  <p>*</p>
  
  <pre><code>Traceback (most recent call last):   File "/home/c4pta1n/.local/bin/pip", line 7, in &lt;module&gt;
      from pip._internal import main   File "/home/c4pta1n/.local/lib/python2.7/site-packages/pip/_internal/__init__.py", line 42, in &lt;module&gt;
      from pip._internal import cmdoptions   File "/home/c4pta1n/.local/lib/python2.7/site-packages/pip/_internal/cmdoptions.py", line 16, in &lt;module&gt;
      from pip._internal.index import (   File "/home/c4pta1n/.local/lib/python2.7/site-packages/pip/_internal/index.py", line 15, in &lt;module&gt;
      from pip._vendor import html5lib, requests, six   File "/home/c4pta1n/.local/lib/python2.7/site-packages/pip/_vendor/requests/__init__.py", line 86, in &lt;module&gt;
      from pip._vendor.urllib3.contrib import pyopenssl   File "/home/c4pta1n/.local/lib/python2.7/site-packages/pip/_vendor/urllib3/contrib/pyopenssl.py", line 46, in &lt;module&gt;
      import OpenSSL.SSL   File "/usr/local/lib/python2.7/dist-packages/OpenSSL/__init__.py", line 8, in &lt;module&gt;
      from OpenSSL import rand, crypto, SSL   File "/usr/local/lib/python2.7/dist-packages/OpenSSL/crypto.py", line 13, in &lt;module&gt;
      from cryptography.hazmat.primitives.asymmetric import dsa, rsa   File "/usr/local/lib/python2.7/dist-packages/cryptography/hazmat/primitives/asymmetric/__init__.py", line 12, in &lt;module&gt;
      @six.add_metaclass(abc.ABCMeta) AttributeError: 'module' object has no attribute 'add_metaclass'
  </code></pre>
  
  <p>*</p>
  
  <pre><code>pip3 install pip --ignore-installed six
  Traceback (most recent call last):
    File "/usr/local/bin/pip3", line 11, in &lt;module&gt;
      load_entry_point('pip==10.0.1', 'console_scripts', 'pip3')()
    File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 476, in load_entry_point
      return get_distribution(dist).load_entry_point(group, name)
    File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2700, in load_entry_point
      return ep.load()
    File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2318, in load
      return self.resolve()
    File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2324, in resolve
      module = __import__(self.module_name, fromlist=['__name__'], level=0)
    File "/usr/local/lib/python2.7/dist-packages/pip/_internal/__init__.py", line 42, in &lt;module&gt;
      from pip._internal import cmdoptions
    File "/usr/local/lib/python2.7/dist-packages/pip/_internal/cmdoptions.py", line 16, in &lt;module&gt;
      from pip._internal.index import (
    File "/usr/local/lib/python2.7/dist-packages/pip/_internal/index.py", line 15, in &lt;module&gt;
      from pip._vendor import html5lib, requests, six
    File "/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/__init__.py", line 86, in &lt;module&gt;
      from pip._vendor.urllib3.contrib import pyopenssl
    File "/usr/local/lib/python2.7/dist-packages/pip/_vendor/urllib3/contrib/pyopenssl.py", line 46, in &lt;module&gt;
      import OpenSSL.SSL
    File "/usr/local/lib/python2.7/dist-packages/OpenSSL/__init__.py", line 8, in &lt;module&gt;
      from OpenSSL import rand, crypto, SSL
    File "/usr/local/lib/python2.7/dist-packages/OpenSSL/crypto.py", line 13, in &lt;module&gt;
      from cryptography.hazmat.primitives.asymmetric import dsa, rsa
    File "/usr/local/lib/python2.7/dist-packages/cryptography/hazmat/primitives/asymmetric/__init__.py", line 12, in &lt;module&gt;
      @six.add_metaclass(abc.ABCMeta)
  AttributeError: 'module' object has no attribute 'add_metaclass'
  </code></pre>
  
  <p>I have been researching and trying to troubleshoot this issue and I have not been able to narrow down the issue.
  Just prior to noticing this issue I had updated my debian system using the standard repository and had no issues of note, I had also updated a few pip modules using pip3 install --update, I believe the modules I had updated were scapy and requests
  I am unable to use pip for any command that I have tried, even "pip list" or any version of pip through 3.6. 
  I have uninstalled and reinstalled pip, virtualenv, and tried to manually remove the six.add_metaclass-1.0* folder from my distutils folder. 
  Nothing I have tried has created any change that I can see and I am not able to narrow down that any issue that I see written about is indeed similar or related to this specific issue.
  I am hoping to find help to narrow this problem down further, correct it or be pointed in the direction of any information that could help me. </p>