why matplotlib give the error [<matplotlib.lines.Line2D object at 0x0392A9D0>]?

Question

I am using python 2.7.9 on win8. When I tried to plot using matplotlib, the following error showed up:

from pylab import *
plot([1,2,3,4])

[matplotlib.lines.Line2D object at 0x0392A9D0]

I tried the test code "python simple_plot.py --verbose-helpful", and the following warning showed up:

$HOME=C:\Users\XX matplotlib data path C:\Python27\lib\site-packages\matplotlib\mpl-data

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You have the following UNSUPPORTED LaTeX preamble customizations:

Please do not ask for support with these customizations active.

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loaded rc file C:\Python27\lib\site-packages\matplotlib\mpl-data\matplotlibrc matplotlib version 1.4.3 verbose.level helpful interactive is False platform is win32 CACHEDIR=C:\Users\XX.matplotlib Using fontManager instance from C:\Users\XX.matplotlib\fontList.cache backend TkAgg version 8.5 findfont: Matching :family=sans-serif:style=normal:variant=normal:weight=normal:stretch=normal:size=medium to Bitstream Vera Sans (u'C:\Python27\lib\site-packages\matplotlib\mpl-data\fonts\ttf\Vera.ttf') with score of 0.000000

What does this mean? How could I get matplotlib working?

Answer 1

That isn't an error. That has created a plot object but you need to show the window. That's done using pyplot.show(). As stated in the comments, please do not use pylab, but use matplotlib.pyplot instead as pylab has been deprecated. As such, all you have to do is call:

plt.show() 

Just for reproducibility, here's a trace from the Python REPL (using IPython):

In [1]: import matplotlib.pyplot as plt  In [2]: plt.plot([1,2,3,4]) Out[2]: [<matplotlib.lines.Line2D at 0x123245290>]  In [3]: plt.show() 

We get:

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What about in a Jupyter notebook?

If you are using this in a Jupyter notebook, instead of having to use show(), you can place the following in a separate cell after you import matplotlib.pyplot:

%matplotlib inline 

This will automatically draw the figure once you create it and you will not have to use show() after you're done.