title: Python virtualenv ImportError: No module named _vendor
body: <p>I installed virtualenv on my system but when I want to actually create a virtual environment I get the following error:</p>
  
  <pre><code>...
  Successfully installed virtualenv-15.0.3
  $ virtualenv venv
  New python executable in /Users/.../venv/bin/python
  Installing setuptools, pip, wheel...
    Complete output from command /Users/.../venv/bin/python - setuptools pip wheel:
    Traceback (most recent call last):
    File "&lt;stdin&gt;", line 9, in &lt;module&gt;
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pkgutil.py", line 578, in get_data
      loader = get_loader(package)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pkgutil.py", line 464, in get_loader
      return find_loader(fullname)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pkgutil.py", line 474, in find_loader
      for importer in iter_importers(fullname):
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pkgutil.py", line 430, in iter_importers
      __import__(pkg)
  ImportError: No module named _vendor
  ----------------------------------------
  ...Installing setuptools, pip, wheel...done.
  Traceback (most recent call last):
    File "/usr/local/bin/virtualenv", line 11, in &lt;module&gt;
      sys.exit(main())
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 711, in main
      symlink=options.symlink)
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 944, in create_environment
      download=download,
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 900, in install_wheel
      call_subprocess(cmd, show_stdout=False, extra_env=env, stdin=SCRIPT)
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 795, in call_subprocess
      % (cmd_desc, proc.returncode))
  OSError: Command /Users/.../venv/bin/python - setuptools pip wheel failed with error code 1
  </code></pre>
  
  <p>Any suggestions why this fails?</p>