ValueError in matplotlib quando si usa \: LaTeX spaziatura orizzontale

Question

Vedi MWE di seguito:

import matplotlib.pyplot as plt 
import matplotlib.offsetbox as offsetbox 

fig = plt.figure() 
ax = fig.add_subplot(111) 

text1 = r'$a\,=\,{}\pm{}$'.format(0.01, 0.002) # Works. 
text2 = r'$a\;=\,{}\pm{}$'.format(0.01, 0.002) # Works. 
text3 = r'$a\:=\,{}\pm{}$'.format(0.01, 0.002) # Does not work. 

text = text3 
ob = offsetbox.AnchoredText(text, pad=1, loc=6, prop=dict(size=13)) 
ob.patch.set(alpha=0.85) 
ax.add_artist(ob) 

plt.show() 

Mentre text1 e text2 che utilizzano \, e \; spaziatura funzionerà senza problemi, text3 che utilizza \: (vale a dire: l'orizzontale spaziatura situato between the previous two) non riesce con un ValueError:

Traceback (most recent call last): 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_gtk3agg.py", line 42, in on_draw_event 
    self._render_figure(w, h) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_gtk3agg.py", line 32, in _render_figure 
    backend_agg.FigureCanvasAgg.draw(self) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_agg.py", line 469, in draw 
    self.figure.draw(self.renderer) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/artist.py", line 59, in draw_wrapper 
    draw(artist, renderer, *args, **kwargs) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/figure.py", line 1085, in draw 
    func(*args) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/artist.py", line 59, in draw_wrapper 
    draw(artist, renderer, *args, **kwargs) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/axes/_base.py", line 2110, in draw 
    a.draw(renderer) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/offsetbox.py", line 1107, in draw 
    bbox = self.get_window_extent(renderer) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/offsetbox.py", line 1063, in get_window_extent 
    w, h, xd, yd = self.get_extent(renderer) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/offsetbox.py", line 1014, in get_extent 
    w, h, xd, yd = self.get_child().get_extent(renderer) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/offsetbox.py", line 782, in get_extent 
    bbox, info, d = self._text._get_layout(renderer) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/text.py", line 320, in _get_layout 
    ismath=ismath) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_agg.py", line 228, in get_text_width_height_descent 
    self.mathtext_parser.parse(s, self.dpi, prop) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/mathtext.py", line 3005, in parse 
    box = self._parser.parse(s, font_output, fontsize, dpi) 
    File "/usr/local/lib/python2.7/dist-packages/matplotlib/mathtext.py", line 2339, in parse 
    six.text_type(err)])) 
ValueError: 
a\:=\,0.01\pm0.002 
^ 
Unknown symbol: \ (at char 1), (line:1, col:2) 

Perché questa spaziatura LaTeX non viene riconosciuta?

Answer 1

Poiché matplotlib utilizza mathtext come renderer matematico predefinito. Mathtext è un sottoinsieme del normale TeX. È possibile utilizzare full LaTeX con:

from matplotlib import pyplot as plt 
import matplotlib as mpl 
mpl.rcParams['text.usetex'] = True 
mpl.rcParams['text.latex.preamble'] = [r'\usepackage{amsmath}'] #if needed 
plt.plot([1,2,3]) 
plt.title(r"$a\:=\,{}\pm{}$".format(0.01, 0.002)) 
plt.show()