Changed linewidth to 0.1 when binary=False

[scmanjarrez]

The line fig = counter_vs_clock(binary=False) at the start of the chapter9
raises the following exception using matplotlib 3.6.2 (local jupyerlab), however
it runs fine on 3.2.2 (installed on colab):

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/pyplot.py:119, in _draw_all_if_interactive()
    117 def _draw_all_if_interactive():
    118     if matplotlib.is_interactive():
--> 119         draw_all()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/_pylab_helpers.py:132, in Gcf.draw_all(cls, force)
    130 for manager in cls.get_all_fig_managers():
    131     if force or manager.canvas.figure.stale:
--> 132         manager.canvas.draw_idle()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/backend_bases.py:2054, in FigureCanvasBase.draw_idle(self, *args, **kwargs)
   2052 if not self._is_idle_drawing:
   2053     with self._idle_draw_cntx():
-> 2054         self.draw(*args, **kwargs)

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/backends/backend_agg.py:405, in FigureCanvasAgg.draw(self)
    401 # Acquire a lock on the shared font cache.
    402 with RendererAgg.lock, \
    403      (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar
    404       else nullcontext()):
--> 405     self.figure.draw(self.renderer)
    406     # A GUI class may be need to update a window using this draw, so
    407     # don't forget to call the superclass.
    408     super().draw()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:74, in _finalize_rasterization.<locals>.draw_wrapper(artist, renderer, *args, **kwargs)
     72 @wraps(draw)
     73 def draw_wrapper(artist, renderer, *args, **kwargs):
---> 74     result = draw(artist, renderer, *args, **kwargs)
     75     if renderer._rasterizing:
     76         renderer.stop_rasterizing()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:51, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     48     if artist.get_agg_filter() is not None:
     49         renderer.start_filter()
---> 51     return draw(artist, renderer)
     52 finally:
     53     if artist.get_agg_filter() is not None:

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/figure.py:3071, in Figure.draw(self, renderer)
   3068         # ValueError can occur when resizing a window.
   3070 self.patch.draw(renderer)
-> 3071 mimage._draw_list_compositing_images(
   3072     renderer, self, artists, self.suppressComposite)
   3074 for sfig in self.subfigs:
   3075     sfig.draw(renderer)

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/image.py:131, in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    129 if not_composite or not has_images:
    130     for a in artists:
--> 131         a.draw(renderer)
    132 else:
    133     # Composite any adjacent images together
    134     image_group = []

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:51, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     48     if artist.get_agg_filter() is not None:
     49         renderer.start_filter()
---> 51     return draw(artist, renderer)
     52 finally:
     53     if artist.get_agg_filter() is not None:

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/axes/_base.py:3107, in _AxesBase.draw(self, renderer)
   3104         a.draw(renderer)
   3105     renderer.stop_rasterizing()
-> 3107 mimage._draw_list_compositing_images(
   3108     renderer, self, artists, self.figure.suppressComposite)
   3110 renderer.close_group('axes')
   3111 self.stale = False

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/image.py:131, in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    129 if not_composite or not has_images:
    130     for a in artists:
--> 131         a.draw(renderer)
    132 else:
    133     # Composite any adjacent images together
    134     image_group = []

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:51, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     48     if artist.get_agg_filter() is not None:
     49         renderer.start_filter()
---> 51     return draw(artist, renderer)
     52 finally:
     53     if artist.get_agg_filter() is not None:

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/lines.py:799, in Line2D.draw(self, renderer)
    796 lc_rgba = mcolors.to_rgba(self._color, self._alpha)
    797 gc.set_foreground(lc_rgba, isRGBA=True)
--> 799 gc.set_dashes(*self._dash_pattern)
    800 renderer.draw_path(gc, tpath, affine.frozen())
    801 gc.restore()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/backend_bases.py:926, in GraphicsContextBase.set_dashes(self, dash_offset, dash_list)
    923         raise ValueError(
    924             "All values in the dash list must be non-negative")
    925     if dl.size and not np.any(dl > 0.0):
--> 926         raise ValueError(
    927             'At least one value in the dash list must be positive')
    928 self._dashes = dash_offset, dash_list

ValueError: At least one value in the dash list must be positive

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/IPython/core/formatters.py:338, in BaseFormatter.__call__(self, obj)
    336     pass
    337 else:
--> 338     return printer(obj)
    339 # Finally look for special method names
    340 method = get_real_method(obj, self.print_method)

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/IPython/core/pylabtools.py:152, in print_figure(fig, fmt, bbox_inches, base64, **kwargs)
    149     from matplotlib.backend_bases import FigureCanvasBase
    150     FigureCanvasBase(fig)
--> 152 fig.canvas.print_figure(bytes_io, **kw)
    153 data = bytes_io.getvalue()
    154 if fmt == 'svg':

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/backend_bases.py:2314, in FigureCanvasBase.print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, pad_inches, bbox_extra_artists, backend, **kwargs)
   2308     renderer = _get_renderer(
   2309         self.figure,
   2310         functools.partial(
   2311             print_method, orientation=orientation)
   2312     )
   2313     with getattr(renderer, "_draw_disabled", nullcontext)():
-> 2314         self.figure.draw(renderer)
   2316 if bbox_inches:
   2317     if bbox_inches == "tight":

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:74, in _finalize_rasterization.<locals>.draw_wrapper(artist, renderer, *args, **kwargs)
     72 @wraps(draw)
     73 def draw_wrapper(artist, renderer, *args, **kwargs):
---> 74     result = draw(artist, renderer, *args, **kwargs)
     75     if renderer._rasterizing:
     76         renderer.stop_rasterizing()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:51, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     48     if artist.get_agg_filter() is not None:
     49         renderer.start_filter()
---> 51     return draw(artist, renderer)
     52 finally:
     53     if artist.get_agg_filter() is not None:

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/figure.py:3071, in Figure.draw(self, renderer)
   3068         # ValueError can occur when resizing a window.
   3070 self.patch.draw(renderer)
-> 3071 mimage._draw_list_compositing_images(
   3072     renderer, self, artists, self.suppressComposite)
   3074 for sfig in self.subfigs:
   3075     sfig.draw(renderer)

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/image.py:131, in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    129 if not_composite or not has_images:
    130     for a in artists:
--> 131         a.draw(renderer)
    132 else:
    133     # Composite any adjacent images together
    134     image_group = []

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:51, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     48     if artist.get_agg_filter() is not None:
     49         renderer.start_filter()
---> 51     return draw(artist, renderer)
     52 finally:
     53     if artist.get_agg_filter() is not None:

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/axes/_base.py:3107, in _AxesBase.draw(self, renderer)
   3104         a.draw(renderer)
   3105     renderer.stop_rasterizing()
-> 3107 mimage._draw_list_compositing_images(
   3108     renderer, self, artists, self.figure.suppressComposite)
   3110 renderer.close_group('axes')
   3111 self.stale = False

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/image.py:131, in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    129 if not_composite or not has_images:
    130     for a in artists:
--> 131         a.draw(renderer)
    132 else:
    133     # Composite any adjacent images together
    134     image_group = []

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/artist.py:51, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     48     if artist.get_agg_filter() is not None:
     49         renderer.start_filter()
---> 51     return draw(artist, renderer)
     52 finally:
     53     if artist.get_agg_filter() is not None:

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/lines.py:799, in Line2D.draw(self, renderer)
    796 lc_rgba = mcolors.to_rgba(self._color, self._alpha)
    797 gc.set_foreground(lc_rgba, isRGBA=True)
--> 799 gc.set_dashes(*self._dash_pattern)
    800 renderer.draw_path(gc, tpath, affine.frozen())
    801 gc.restore()

File ~/side_projects/brain_auth/psychopy/data_alcoholism/venv/lib/python3.8/site-packages/matplotlib/backend_bases.py:926, in GraphicsContextBase.set_dashes(self, dash_offset, dash_list)
    923         raise ValueError(
    924             "All values in the dash list must be non-negative")
    925     if dl.size and not np.any(dl > 0.0):
--> 926         raise ValueError(
    927             'At least one value in the dash list must be positive')
    928 self._dashes = dash_offset, dash_list

ValueError: At least one value in the dash list must be positive

Using 0.1 as line width instead of 0 (matplotlib/matplotlib#8821) seems to avoid the error and doesn't affect the output of the plot.

[dvgodoy]

Hi @scmanjarrez

Thank you for pointing out this behavior of newer matplotlib versions.
The proposed solution works, but it still leaves a barely perceptible line (which has 0.1 width). We could make it even thinner, like 0.001, but I figured that the problem is only raised whenever the line style is dashed. Matplotlib allows 0 width for continuous lines (which would be invisible anyway), but it breaks if the (invisible) line is dashed (go figure...).

The line width should be zero only when arrows are drawn. Then, if it is actually invisible, we can have it "continuous", after all, we're not seeing it anyway :-)

So, one solution would be:

            line = axs[is_clock].plot(*arrow_coords.T, c=color, lw=0 if draw_arrows else 2, 
                                      alpha=alpha, linestyle='--' if (alpha < 1) and (not draw_arrows) else '-')[0]

If you update the PR accordingly, I can merge it. If not, I can make the change myself too, it's your call :-)

Best,
Daniel

[scmanjarrez]

Thank you Daniel, I've committed the proposed fix.