title: Why does virtualenv throw an error when I try to define the python version as 2.7?
body: <p>I tried to create a new virtualenv directory with <code>sudo virtualenv curdir -p /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7</code> and it threw the following error:</p>
  
  <pre><code>Running virtualenv with interpreter /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
  Traceback (most recent call last):
    File "/usr/local/bin/virtualenv", line 9, in &lt;module&gt;
      load_entry_point('virtualenv==1.6.4', 'console_scripts', 'virtualenv')()
    File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages/virtualenv.py", line 785, in main
      popen = subprocess.Popen([interpreter, file] + sys.argv[1:], env=env)
    File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/subprocess.py", line 741, in __init__
      restore_signals, start_new_session)
    File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/subprocess.py", line 1356, in _execute_child
      raise child_exception_type(errno_num, err_msg)
  OSError: [Errno 13] Permission denied
  </code></pre>
  
  <p>I understand that I was not allowed to do that, but why? python 2.7 is located there and I want to use it. Is there any way to use it in my virtualenv?</p>
  
  <p>I hope that this isn't too basic of a question. I am still pretty new to Unix command line.</p>