Prototype of an extension to provide acess to virtual python environment on an IPython notebook cell

test_virtualenvmagic.py

# -*- coding: utf-8 -*-
"""
Tests for the virtualenvmagic extension
Author: Flávio Codeço Coelho - @fccoelho
"""

import os
import nose.tools as nt


def setup():
    ip = get_ipython()
    ip.extension_manager.load_extension('virtualenvmagic')
    
def test_virtualenv():
    ip = get_ipython()
    result = ip.run_cell_magic('virtualenv','pypyEnv','import sys;print sys.version')
    nt.assert_true('PyPy' in result)
    
    

virtualenvmagic.py

# -*- coding: utf-8 -*-
"""
Virtualenv magic
Requires virtualenv and virtualenv Wrapper
Author: Flávio Codeço Coelho - @fccoelho
Thanks to @turicas for helpful tips
"""
import sys
import os
import shlex
from subprocess import Popen, PIPE
from IPython.core.magic import cell_magic


@cell_magic('virtualenv')
def virtualenv(line, cell):
    """
    This magic enables the execution of code in a cell on a
    pre-existing virtual env. It Requires Virtualenv and VirtualenvWrapper
    to be installed in the system.
    The virtual env to be used must be created in advance.
    
    Usage
    =====
    To activate this magic just write at the top of the cell:
    
        %%virtualenv my_env
        import sys
        print sys.version
        
    
    """
    if not os.path.exists(os.environ['WORKON_HOME']+'/'+line):
        print >> sys.stderr, "Environment {} does no exist.".format(line)
        return
    env_activate_cmd = 'bash -c "source {}/{}/bin/activate && python -"'.format(os.environ['WORKON_HOME'],line)
    cmd = shlex.split(env_activate_cmd)
    p = Popen(cmd, stdout=PIPE, stderr=PIPE, stdin=PIPE)
    out,err = p.communicate(cell)
    p.wait()
    if err:
        print >> sys.stderr, err
    return out

_loaded = False

def load_ipython_extension(ip):
    """Load the extension in IPython."""
    global _loaded
    if not _loaded:
        if 'WORKON_HOME' in os.environ:
            ip.register_magic_function(virtualenv, 'cell')
            _loaded = True
        else:
            print >> sys.stderr, "You must have Virtualenv and VirtualenvWrapper installed."

Rather than calling get_ipython() or InteractiveShell(), an IPython extension should offer a load_ipython_extension(ip) method, which will be called with the shell object when it's loaded. Docs: http://ipython.org/ipython-doc/stable/config/extensions/index.html

(The rationale for this is that we have a long term goal to allow more than one InteractiveShell object in the same process - so we're trying not to treat it like a singleton)

I'll study other extensions and modify my code to conform.
thanks @takluyver

Thanks @turicas for the tip on how to make the bash command work...

@fccoelho, PEP8, please! :-)