I have been through the process of installing matplotlib on my Ubuntu 12.04 computer. However, when I try to run a test program, I get the following error:

Traceback (most recent call last):

  File "../py33/test.py", line 2, in <module>

    import matplotlib.pyplot as plt

ImportError: No module named 'matplotlib'

I am trying a sample program from matplotlib's website (basic_example). I just don't understand why it says there is not module matplotlib, even though I have definitely installed it (using sudo apt-get install python-matplotlib, and have done sudo apt-get build-dep python-matplotlib; I also tried pip install matplotlib, as I was told to do that, after installing Python itself, if I wanted to install other binaries).