在 virtualenv 中找不到 Python 模块

我无法让模块在我的虚拟环境中运行。以熊猫为例：

随着虚拟环境的开启，我运行yolk -l并返回（缩短版）：

(basicpython)xxxx@LinuxBox:~/pythonprojects/basicpython$ yolk -l
Python          - 2.7.3        - active development (/usr/lib/python2.7/lib-dynload)
numpy           - 1.6.1        - active 
pandas          - 0.7.0        - active development (/usr/lib/pymodules/python2.7)

所以它就在那里。但是当我尝试激活该模块时出现错误：

(basicpython)xxxxx@LinuxBox:~/pythonprojects/basicpython$ python
Python 2.7.3 (default, Sep 26 2013, 20:08:41) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
ImportError: No module named pandas

当我关闭虚拟环境并执行相同的操作时，它会起作用：

(basicpython)xxxxx@LinuxBox:~/pythonprojects/basicpython$ deactivate
xxxx@LinuxBox:~/pythonprojects/basicpython$ python
Python 2.7.3 (default, Sep 26 2013, 20:08:41) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> pd
<module 'pandas' from '/usr/lib/pymodules/python2.7/pandas/__init__.pyc'>

知道为什么会发生这种情况（我是否错过了 virtualenv 的安装步骤？）

编辑：我在虚拟环境中安装了 pandas 和其他库，这是否不会将它们安装在环境中？

编辑2：我尝试在虚拟环境中重新安装软件包，系统表示它们已经存在：

(basicpython)xxxx@LinuxBox:~/pythonprojects/basicpython$ sudo apt-get install               
python-numpy python-scipy python-matplotlib ipython ipython-notebook python-pandas       python-sympy python-nose
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  python-nose is already the newest version.
  python-numpy is already the newest version.
  ipython is already the newest version.
  ipython-notebook is already the newest version.
  python-matplotlib is already the newest version.
  python-pandas is already the newest version.
  python-scipy is already the newest version.
  python-sympy is already the newest version.
  The following packages were automatically installed and are no longer required:
   linux-headers-3.2.0-55-generic-pae gir1.2-ubuntuoneui-3.0 linux-headers-3.2.0-55       libubuntuoneui-3.0-1
   Use 'apt-get autoremove' to remove them.
   0 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.
  (basicpython)xxxxx@LinuxBox:~/pythonprojects/basicpython$ 

据我了解，这里有两个问题：

1. Yolk 未安装在您的 virtualenv 中。由于它从全局模块中获取蛋黄，因此您将获得所有全局包的列表。有关此问题的信息请检查此问题：virtualenv蛋黄问题 https://stackoverflow.com/questions/2742980/virtualenv-yolk-problem

2. Pandas 模块似乎也没有安装在您的 virtualenv 中（我猜您使用了默认的 virtualenv 创建，它不使用任何站点包）。检查这一点的快速方法是pip freeze。你应该继续在你的 virtualenv 中安装 pandas (pip install pandas），然后查看是否出现相同的行为。