在我的ubuntu 16.04系统中，pyplot imshow（）曾经在系统python和虚拟环境（针对tensorflow）中都能正常工作。如果文件aa.py包含

import matplotlib.pyplot as p
p.plot(range(20),range(20))
p.show()

我运行python aa.py时运行正常。 （我看到一个图）。但是当我激活虚拟环境并在其中运行python aa.py时，会看到以下错误：

Traceback (most recent call last):
  File "aa.py",line 1,in <module>
    import matplotlib.pyplot as p
  File "/home/ckim/venv2/lib/python2.7/site-packages/matplotlib/pyplot.py",line 115,in <module>
    _backend_mod,new_figure_manager,draw_if_interactive,_show = pylab_setup()
  File "/home/ckim/venv2/lib/python2.7/site-packages/matplotlib/backends/__init__.py",line 62,in pylab_setup
    [backend_name],0)
  File "/home/ckim/venv2/lib/python2.7/site-packages/matplotlib/backends/backend_tkagg.py",line 4,in <module>
    from . import tkagg  # Paint image to Tk photo blitter extension.
  File "/home/ckim/venv2/lib/python2.7/site-packages/matplotlib/backends/tkagg.py",line 5,in <module>
    from six.moves import tkinter as Tk
  File "/home/ckim/venv2/lib/python2.7/site-packages/six.py",line 203,in load_module
    mod = mod._resolve()
  File "/home/ckim/venv2/lib/python2.7/site-packages/six.py",in _resolve
    return _import_module(self.mod)
  File "/home/ckim/venv2/lib/python2.7/site-packages/six.py",line 82,in _import_module
    __import__(name)
  File "/usr/lib/python2.7/lib-tk/Tkinter.py",line 42,in <module>
    raise ImportError,str(msg) + ',please install the python-tk package'
ImportError: No module named _tkinter,please install the python-tk package

我想我已经解决了这个问题，但是忘记了我是怎么做到的。