Scikit-learn已安装但未找到，

Question

我已经安装了scipy，numpy和scikit-learn但是当我在python shell上时我无法导入sklearn，它说没有具有该名称的模块：

Requirement already up-to-date: numpy in .../lib/python2.7/site-packages
Requirement already up-to-date: scipy in .../site-packages
Requirement already up-to-date: scikit-learn in ...7/site-packages

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

可能是什么问题？