Unable to "import matplotlib.pyplot as plt" in virtualenv

I am working with flask in a virtual environment. I was able to install matplotlib with pip, and I can import matplotlib in a Python session. However, when I import it as

    matplotlib.pyplot as plt

I get the following error:

    >>> import matplotlib.pyplot as plt

    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "//anaconda/envs/myenv/lib/python2.7/site-packages/matplotlib/pyplot.py", line 109, in <module>
        _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
      File "//anaconda/envs/myenv/lib/python2.7/site-packages/matplotlib/backends/__init__.py", line 32, in pylab_setup
      File "//anaconda/envs/myenv/lib/python2.7/site-packages/matplotlib/backends/backend_macosx.py", line 24, in <module>
        from matplotlib.backends import _macosx
    RuntimeError: Python is not installed as a framework. The Mac OS X backend will not be able to function correctly if Python is not installed as a framework. See the Python documentation for more information on installing Python as a framework on Mac OS X. Please either reinstall Python as a framework, or try one of the other backends.

I am confused about why it asks me to install Python as framework. Doesn't it already exists? What does it mean to "install Python as framework", and how do I install it?

This solution worked for me. If you already installed matplotlib using pip on your virtual environment, you can just type the following:

    $ cd ~/.matplotlib
    $ nano matplotlibrc

And then, write backend: TkAgg in there. If you need more information, just go to the solution link.

From: stackoverflow.com/q/29433824