title: Using PIP to download a Python Package. Permission error
body: <p>I'm using PIP to get a package I need for Python but I'm getting a permission error even when I'm using "sudo" to access the package.</p>
  
  <p>I'm following the instructions posted <a href="http://www.nltk.org/install.html" rel="nofollow">here</a> on the website for the package.</p>
  
  <pre><code>sudo pip install -U nltk
  Password:
  The directory '/Users/me/Library/Caches/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
  The directory '/Users/me/Library/Caches/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
  Collecting nltk
    Downloading nltk-3.0.5.tar.gz (1.0MB)
      100% |████████████████████████████████| 1.0MB 289kB/s 
  Collecting six&gt;=1.9.0 (from nltk)
    Downloading six-1.9.0-py2.py3-none-any.whl
  Installing collected packages: six, nltk
    Found existing installation: six 1.4.1
      DEPRECATION: Uninstalling a distutils installed project (six) has been deprecated and will be removed in a future version. This is due to the fact that uninstalling a distutils project will only partially uninstall the project.
      Uninstalling six-1.4.1:
  Exception:
  Traceback (most recent call last):
    File "/Library/Python/2.7/site-packages/pip-7.1.2-py2.7.egg/pip/basecommand.py", line 211, in main
      status = self.run(options, args)
    File "/Library/Python/2.7/site-packages/pip-7.1.2-py2.7.egg/pip/commands/install.py", line 311, in run
      root=options.root_path,
    File "/Library/Python/2.7/site-packages/pip-7.1.2-py2.7.egg/pip/req/req_set.py", line 640, in install
      requirement.uninstall(auto_confirm=True)
    File "/Library/Python/2.7/site-packages/pip-7.1.2-py2.7.egg/pip/req/req_install.py", line 716, in uninstall
      paths_to_remove.remove(auto_confirm)
    File "/Library/Python/2.7/site-packages/pip-7.1.2-py2.7.egg/pip/req/req_uninstall.py", line 125, in remove
      renames(path, new_path)
    File "/Library/Python/2.7/site-packages/pip-7.1.2-py2.7.egg/pip/utils/__init__.py", line 315, in renames
      shutil.move(old, new)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 302, in move
      copy2(src, real_dst)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 131, in copy2
      copystat(src, dst)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 103, in copystat
      os.chflags(dst, st.st_flags)
  OSError: [Errno 1] Operation not permitted: '/tmp/pip-KICJWB-uninstall/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/six-1.4.1-py2.7.egg-info'
  </code></pre>
  
  <p>It says my parent directory is not owned by me ... but I'm the only user on my computer. So I don't know what is going on here.</p>
  
  <p>Thanks,</p>