title: ipdb is triggering ImportError
body: <p>ipdb is triggering an import error for me when I run my Django site locally.  I'm working on Python 2.7 and within a virtual environment.</p>
  
  <p><code>which ipdb</code> shows the path <code>(/usr/local/bin/ipdb)</code>, as does <code>which ipython</code>, which surprised me since I thought it should show my venv path (but shouldn't it work if it's global, anyway?).  So I tried <code>pip install --target=/path/to/venv ipdb</code> and now it shows up in <code>pip freeze</code> (which it didn't before) but still gives me an import error.  </p>
  
  <p><code>which pip</code> gives <code>/Users/myname/.virtualenvs/myenv/bin/pip/</code> </p>
  
  <p>My path:  <code>/Users/myname/.virtualenvs/myenv/bin:/Users/myname/.venvburrito/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/myname/bin:/usr/local/bin</code></p>
  
  <p>Sys.path:
  <code>'/Users/myname/Dropbox/myenv', '/Users/myname/.venvburrito/lib/python2.7/site-packages/pip-1.4.1-py2.7.egg', '/Users/myname/.venvburrito/lib/python2.7/site-packages', '/Users/myname/.venvburrito/lib/python2.7/site-packages/setuptools-8.2-py2.7.egg', '/Users/myname/.virtualenvs/myenv/lib/python27.zip', '/Users/myname/.virtualenvs/myenv/lib/python2.7', '/Users/myname/.virtualenvs/myenv/lib/python2.7/plat-darwin', '/Users/myname/.virtualenvs/myenv/lib/python2.7/plat-mac', '/Users/myname/.virtualenvs/myenv/lib/python2.7/plat-mac/lib-scriptpackages', '/Users/myname/.virtualenvs/myenv/Extras/lib/python', '/Users/myname/.virtualenvs/myenv/lib/python2.7/lib-tk', '/Users/myname/.virtualenvs/myenv/lib/python2.7/lib-old', '/Users/myname/.virtualenvs/myenv/lib/python2.7/lib-dynload', '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7', '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin', '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk', '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac', '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages', '/Users/myname/.virtualenvs/myenv/lib/python2.7/site-packages']</code></p>
  
  <p>If I run ipdb from the terminal, it works fine.  I've tried restarting my terminal.</p>
  
  <p>Stacktrace:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/Users/myname/.virtualenvs/myenv/lib/python2.7/site-packages/django/core/handlers/base.py", line 149, in get_response
      response = self.process_exception_by_middleware(e, request)
    File "/Users/myname/.virtualenvs/myenv/lib/python2.7/site-packages/django/core/handlers/base.py", line 147, in get_response
      response = wrapped_callback(request, *callback_args, **callback_kwargs)
    File "/Users/myname/.virtualenvs/myenv/lib/python2.7/site-packages/django/views/generic/base.py", line 68, in view
      return self.dispatch(request, *args, **kwargs)
    File "/Users/myname/.virtualenvs/myenv/lib/python2.7/site-packages/django/views/generic/base.py", line 88, in dispatch
      return handler(request, *args, **kwargs)
    File "/Users/myname/.virtualenvs/myenv/lib/python2.7/site-packages/django/views/generic/base.py", line 157, in get
      context = self.get_context_data(**kwargs)
    File "/Users/myname/Dropbox/blog/views.py", line 22, in get_context_data
      import ipdb; ipdb.set_trace()
  ImportError: No module named ipdb
  </code></pre>