title: Python import-site error with multiple versions
body: <p>I'm using a shared machine. I'm trying to install Python 2.6 for a project that is using Pysco (unsupported on 2.7), and there is an existing install of 2.7 on the machine that I cannot remove without breaking other people's projects.</p>
  
  <p>I'm using 32-bit binaries of Python on Windows 7.</p>
  
  <p>When I try to start Python 2.6, I get this error:</p>
  
  <pre><code>'import-site' failed; use -v for traceback
  </code></pre>
  
  <p>It looks like Python 2.6 is trying to import modules from Python 2.7, which is causing the failure (see output below). Does anybody know what might be causing this, and how it could be fixed? Thanks!</p>
  
  <p>Running with the -v option gives the following output</p>
  
  <pre><code># installing zipimport hook
  import zipimport # builtin
  # installed zipimport hook
  # C:\Python27\Lib\site.pyc matches C:\Python27\Lib\site.py
  import site # precompiled from C:\Python27\Lib\site.pyc
  # C:\Python27\Lib\os.pyc matches C:\Python27\Lib\os.py
  import os # precompiled from C:\Python27\Lib\os.pyc
  import errno # builtin
  import nt # builtin
  # C:\Python27\Lib\ntpath.pyc matches C:\Python27\Lib\ntpath.py
  import ntpath # precompiled from C:\Python27\Lib\ntpath.pyc
  # C:\Python27\Lib\stat.pyc matches C:\Python27\Lib\stat.py
  import stat # precompiled from C:\Python27\Lib\stat.pyc
  # C:\Python27\Lib\genericpath.pyc matches C:\Python27\Lib\genericpath.py
  import genericpath # precompiled from C:\Python27\Lib\genericpath.pyc
  # C:\Python27\Lib\warnings.pyc matches C:\Python27\Lib\warnings.py
  import warnings # precompiled from C:\Python27\Lib\warnings.pyc
  # C:\Python27\Lib\linecache.pyc matches C:\Python27\Lib\linecache.py
  import linecache # precompiled from C:\Python27\Lib\linecache.pyc
  # C:\Python27\Lib\types.pyc matches C:\Python27\Lib\types.py
  import types # precompiled from C:\Python27\Lib\types.pyc
  # C:\Python27\Lib\UserDict.pyc matches C:\Python27\Lib\UserDict.py
  import UserDict # precompiled from C:\Python27\Lib\UserDict.pyc
  # C:\Python27\Lib\_abcoll.pyc matches C:\Python27\Lib\_abcoll.py
  import _abcoll # precompiled from C:\Python27\Lib\_abcoll.pyc
  # C:\Python27\Lib\abc.pyc matches C:\Python27\Lib\abc.py
  import abc # precompiled from C:\Python27\Lib\abc.pyc
  # C:\Python27\Lib\_weakrefset.pyc matches C:\Python27\Lib\_weakrefset.py
  import _weakrefset # precompiled from C:\Python27\Lib\_weakrefset.pyc
  import _weakref # builtin
  'import site' failed; traceback:
  Traceback (most recent call last):
    File "C:\Python27\Lib\site.py", line 62, in &lt;module&gt;
      import os
    File "C:\Python27\Lib\os.py", line 398, in &lt;module&gt;
      import UserDict
    File "C:\Python27\Lib\UserDict.py", line 84, in &lt;module&gt;
      _abcoll.MutableMapping.register(IterableUserDict)
    File "C:\Python27\Lib\abc.py", line 109, in register
      if issubclass(subclass, cls):
    File "C:\Python27\Lib\abc.py", line 151, in __subclasscheck__
      if subclass in cls._abc_cache:
    File "C:\Python27\Lib\_weakrefset.py", line 69, in __contains__
      return ref(item) in self.data
  TypeError: cannot create weak reference to 'classobj' object
  </code></pre>