当我尝试运行来自www.matplotlib.org的非常简单的代码片段时，
from matplotlib import rc
rc('font',**{'family':'sans-serif','sans-serif':['Helvetica']})
## for Palatino and other serif fonts use:
#rc('font',**{'family':'serif','serif':['Palatino']})
rc('text', usetex=True)
import numpy as np
import matplotlib.pyplot as plt
# Example data
t = np.arange(0.0, 1.0 + 0.01, 0.01)
s = np.cos(4 * np.pi * t) + 2
plt.rc('text', usetex=True)
plt.rc('font', family='serif')
plt.plot(t, s)
plt.xlabel(r'\textbf{time} (s)')
plt.ylabel(r'\textit{voltage} (mV)',fontsize=16)
plt.title(r"\TeX\ is Number "
r"$\displaystyle\sum_{n=1}^\infty\frac{-e^{i\pi}}{2^n}$!",
fontsize=16, color='gray')
# Make room for the ridiculously large title.
plt.subplots_adjust(top=0.8)
plt.savefig('tex_demo')
plt.show()
这非常不寻常，因为这段代码之前曾经运行过，但我现在无法弄清楚问题所在。我收到的错误信息非常庞大，如下所示。有人知道问题可能是什么吗？
谢谢！
Traceback (most recent call last): File "/Users/evan/anaconda3/lib/python3.6/site-packages/IPython/core/formatters.py", line 332, in call return printer(obj) File "/Users/evan/anaconda3/lib/python3.6/site-packages/IPython/core/pylabtools.py", line 237, in png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs)) File "/Users/evan/anaconda3/lib/python3.6/site-packages/IPython/core/pylabtools.py", line 121, in print_figure fig.canvas.print_figure(bytes_io, **kw) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/backend_bases.py", line 2216, in print_figure **kwargs) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/backends/backend_agg.py", line 507, in print_png FigureCanvasAgg.draw(self) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/backends/backend_agg.py", line 430, in draw self.figure.draw(self.renderer) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/artist.py", line 55, in draw_wrapper return draw(artist, renderer, *args, **kwargs) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/figure.py", line 1299, in draw renderer, self, artists, self.suppressComposite) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/image.py", line 138, in _draw_list_compositing_images a.draw(renderer) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/artist.py", line 55, in draw_wrapper return draw(artist, renderer, *args, **kwargs) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/axes/_base.py", line 2437, in draw mimage._draw_list_compositing_images(renderer, self, artists) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/image.py", line 138, in _draw_list_compositing_images a.draw(renderer) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/artist.py", line 55, in draw_wrapper return draw(artist, renderer, *args, **kwargs) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/axis.py", line 1135, in draw renderer) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/axis.py", line 1075, in _get_tick_bboxes extent = tick.label1.get_window_extent(renderer) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/text.py", line 933, in get_window_extent bbox, info, descent = self._get_layout(self._renderer) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/text.py", line 308, in _get_layout ismath=False) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/backends/backend_agg.py", line 226, in get_text_width_height_descent s, fontsize, renderer=self) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/texmanager.py", line 602, in get_text_width_height_descent dvifile = self.make_dvi(tex, fontsize) File "/Users/evan/anaconda3/lib/python3.6/site-packages/matplotlib/texmanager.py", line 393, in make_dvi stderr=subprocess.STDOUT) File "/Users/evan/anaconda3/lib/python3.6/subprocess.py", line 336, in check_output **kwargs).stdout File "/Users/evan/anaconda3/lib/python3.6/subprocess.py", line 403, in run with Popen(*popenargs, **kwargs) as process: File "/Users/evan/anaconda3/lib/python3.6/subprocess.py", line 709, in __init__ restore_signals, start_new_session) File "/Users/evan/anaconda3/lib/python3.6/subprocess.py", line 1344, in _execute_child raise child_exception_type(errno_num, err_msg, err_filename) FileNotFoundError: [Errno 2] No such file or directory