[SOLVED] Module import error in virtualenv but pip list --local shows it

Issue

I'm wondering about the following importError which I can't get ride off. I have a local virtualenv (venv) in which I've installed multiple modules:

(venv) stam@stam:~$ pip list --local

cryptography (1.5.2)
cvxopt (1.1.9)
cycler (0.10.0)
Cython (0.25.1)
matplotlib (1.5.3)
more-itertools (2.2)
ndg-httpsclient (0.4.2)
numpy (1.11.2)
pandas (0.19.0)
paramiko (1.15.2)
Pillow (2.8.1)
pip (8.1.2)
psycopg2 (2.6)
python-apt (0.9.3.12)
python-dateutil (2.5.3)
python-debian (0.1.27)
scipy (0.18.1)
setuptools (28.6.1)
simplejson (3.8.2)
urllib3 (1.9.1)
wheel (0.24.0)
You are using pip version 8.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
(venv) stam@stam:~$ 

now starting a python interpreter and trying to import cvxopt (note it is in the list above) gives me a importError. Why is this? I'm using the right python version, I work on the venv so everything should work out of the box.

(venv) stam@stam:~$ python
Python 2.7.9 (default, Aug 13 2016, 16:41:35) 
[GCC 4.9.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cvxopt
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named cvxopt
>>> 

I'm a bit lost and don't know how exactly I can resolve this issue. It seems the right python version is started, at least the one I've attached to the virtualenv.

Additional outps asked for in the comments

(venv) stam@stam:~$ which python
/usr/bin/python
(venv) stam@stam:~$ which pip
/usr/local/bin/pip

Solution

Based on the output from which it seems clear that your python and pip belong to two different instances. So all libraries you install will be installed for some other python instance.

The acute fix is to force pip to run through your specified interpreter:

python -m pip list --local
python -m pip install cvxopt

Answered By - Harald Nordgren