Pycharm error while importing matplotlib.pyplot as plt

Question

Pycharm error while importing matplotlib.pyplot as plt

I am using pycharm for python on Windows 8. I installed the matplotlib package. I use python 2.7 when I do import matplotlib , there is no error.
However, if I do matplotlib.pyplot as plt , I get the following errors:

        Traceback (most recent call last):
  File "C:/Users/PiyushSudip/PycharmProjects/myFirst/test1.py", line 1, in <module>
    import matplotlib.pyplot as plt
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 23, in <module>
    from matplotlib.figure import Figure, figaspect
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 18, in <module>
    from axes import Axes, SubplotBase, subplot_class_factory
  File "C:\Python27\lib\site-packages\matplotlib\axes\__init__.py", line 4, in <module>
    from ._subplots import *
  File "C:\Python27\lib\site-packages\matplotlib\axes\_subplots.py", line 10, in <module>
    from matplotlib.axes._axes import Axes
  File "C:\Python27\lib\site-packages\matplotlib\axes\_axes.py", line 18, in <module>
    from matplotlib.cbook import _string_to_bool, mplDeprecation
ImportError: cannot import name _string_to_bool