Trouble getting Virtualenv to Import Numpy

Question

I am having trouble with all libraries, but let me focus on numpy. If I am outside a virtualenv, I can go into the Python interpreter and do:

import numpy

and that works. But if I got into a virtualenv and try it:

$ workon test
(test):~/Project/test$ python

>>> import numpy
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named numpy

After hours of Googling I believe the problem must be in my understanding of virtualenv and virtualenvwrapper. I have tried the obvious:

(test):~/Projects/test$ pip install numpy

but I got the error:

SystemError: Cannot compile 'Python.h'. Perhaps you need to install python-dev|python-devel.

I also tried doing sudo apt-get install python-dev but got the errors:

The following packages have unmet dependencies:
 python-dev : Depends: python2.7-dev (>= 2.7.3) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

I am running Python2.7.3 on Ubuntu 12.04 and have PyDev (no virtualenv) running with a project that currently imports libraries (like numpy) with no trouble. I have tried using the Ubuntu Software Center to install python-dev, but I get the same errors.

Answer 1

virtualenv by default doesn't let you import packages from the global environment. Use [mk]virtualenv --system-site-packages to allow it to import system packages.

python-dev is a system package, so the pip error is expected. Not sure about the apt error, but you could ask on askubuntu.com to try to resolve it.