importmatplotlib.pyplotaspltx= [0,1]plt.plot(x,x,ls='--',lw=0)plt.show()

Traceback (most recent call last):  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1489, in __call__    return self.func(*args)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/backends/backend_tkagg.py", line 280, in resize    self.show()  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/backends/backend_tkagg.py", line 351, in draw    FigureCanvasAgg.draw(self)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/backends/backend_agg.py", line 464, in draw    self.figure.draw(self.renderer)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/artist.py", line 63, in draw_wrapper    draw(artist, renderer, *args, **kwargs)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/figure.py", line 1144, in draw    renderer, self, dsu, self.suppressComposite)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images    a.draw(renderer)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/artist.py", line 63, in draw_wrapper    draw(artist, renderer, *args, **kwargs)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/axes/_base.py", line 2426, in draw    mimage._draw_list_compositing_images(renderer, self, dsu)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images    a.draw(renderer)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/artist.py", line 63, in draw_wrapper    draw(artist, renderer, *args, **kwargs)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/lines.py", line 822, in draw    drawFunc(renderer, gc, tpath, affine.frozen())  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/lines.py", line 1267, in _draw_lines    self._lineFunc(renderer, gc, path, trans)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/lines.py", line 1297, in _draw_dashed    gc.set_dashes(self._dashOffset, self._dashSeq)  File "/home/chenyh/.local/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 1009, in set_dashes    raise ValueError("All values in the dash list must be positive")ValueError: All values in the dash list must be positive