(Linux) make iPython virtual env aware

ipython-virtualenv.py

#------------------------------------------------------------------------------
# Make things VirtualEnv aware (Linux version). 
# More info: http://www.swegler.com/becky/blog/2011/08/28/python-django-mysql-on-windows-7-part-3-ipython-virtual-environments/
# add this to the end of ipython_config
# (or course, for virtualenvs created via --no-site-packages, it would
# be much easier just to install iPython)
#
# Also consider sourcing this file from ipython_config with execfile().
#
#------------------------------------------------------------------------------
import sys
import site 
from os import environ 
from os.path import join 

#Is a virtual envrionment currently activated?.  Checking VIRTUAL_ENV (see below)
#didn't work b/c that variable wasn't being cleared upon environment deactivation. 
#So started using the very hacky method of checking for parens in the command prompt.

#if 'VIRTUAL_ENV' in environ: 
if '(' in environ.get('PS1') and ')' in environ.get('PS1'): 
    pythondir = 'python%i.%i' % (sys.version_info[0], sys.version_info[1])
    virtual_env = join(environ.get('VIRTUAL_ENV'), 'lib', pythondir, 'site-packages')
    ALLDIRS = [virtual_env]
    
    #sys.path is the search path for Python modules. 
    prev_sys_path = list(sys.path)    
    
    #Loop through virtual environment's site-packages, adding each directory to the 
    #import path. Note: important to use site.addsitedir instead of adding directly
    #to syspath. Latter method will not interpret .pth files in site-packages dir.
    for directory in ALLDIRS:
        site.addsitedir(directory)
    
    #Adddsitedir appends to the end of sys.path. Now to need to re-order
    #sys.path, putting new directories at the front to ensure virtualenv
    #modules take precedence over those in main python installation
    new_sys_path = []
    for item in list(sys.path):
        if item not in prev_sys_path:
            new_sys_path.append(item)
            sys.path.remove(item)
    sys.path[:0] = new_sys_path
    
else:
    virtual_env = 'none'

print 'VIRTUAL_ENV ->', virtual_env 
del virtual_env 
del site, environ, join, pythondir