Non-ASCII characters in Matplotlib

I have a problem displaying non-ASCII characters in Matplotlib, these characters are rendered as small boxes instead of a proper font, it looks like (I filled these boxes with red paint to hightlight them):

How do I fix it?

A related question is Accented characters in Matplotlib.

This problem may actually have a couple of different causes:

The default font does not include these glyphs

You may change the default font using the following (before any plotting is done!)

matplotlib.rc('font', family='Arial')

In some versions of matplotlib you'll have to set the family:

matplotlib.rc('font', **{'sans-serif' : 'Arial',
                         'family' : 'sans-serif'})

(Note that because sans-serif contains a hyphen inside the **{} syntax, it is actually necessary.)

The first command changes the sans-serif font family to contain only one font (in my case it was Arial), the second sets the default font family to sans-serif.

Other options are included in the documentation.

You have improperly created/passed string objects into Matplotlib

Even if the font contains proper glyphs, if you forgot to use u to create Unicode constants, Matplotlib will have this behaviour:

plt.xlabel("Średnia odległość między stacjami wsparcia a modelowaną [km]")

So you need to add u:

plt.xlabel(u"Średnia odległość między stacjami wsparcia a modelowaną [km]")

Another cause is that you forgot to put a UTF-8 magic comment on top of the file (I read that this might be the source of the problem):

# -*- coding: utf-8 -*-