[Bug]: Error when using path effect with a PolyCollection

[jvierstra]

Bug summary

When trying to add a shadow to a "fill_between", I get the following error: "
SystemError: new style getargs format but argument is not a tuple"

I fixed it by changing the following code in "patheffects.py"

Lines: 100

 def draw_path(self, gc, tpath, affine, rgbFace=None):
        if rgbFace is not None:
            rgbFace = tuple(rgbFace)
        for path_effect in self._path_effects:
            path_effect.draw_path(self._renderer, gc, tpath, affine, rgbFace)

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np
​
import matplotlib.patheffects as mpatheffects

x = np.arange(100)
y = x.copy()

p = plt.fill_between(x, 0, y)
p.set_path_effects([mpatheffects.withSimplePatchShadow()])

Actual outcome

/home/jvierstra/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/seaborn/categorical.py:1296: UserWarning: 59.2% of the points cannot be placed; you may want to decrease the size of the markers or use stripplot.
  warnings.warn(msg, UserWarning)
/home/jvierstra/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/seaborn/categorical.py:1296: UserWarning: 41.7% of the points cannot be placed; you may want to decrease the size of the markers or use stripplot.
  warnings.warn(msg, UserWarning)
---------------------------------------------------------------------------
SystemError                               Traceback (most recent call last)
~/.local/lib/python3.9/site-packages/IPython/core/formatters.py in __call__(self, obj)
    339                 pass
    340             else:
--> 341                 return printer(obj)
    342             # Finally look for special method names
    343             method = get_real_method(obj, self.print_method)

~/.local/lib/python3.9/site-packages/IPython/core/pylabtools.py in <lambda>(fig)
    250         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
    251     if 'retina' in formats or 'png2x' in formats:
--> 252         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))
    253     if 'jpg' in formats or 'jpeg' in formats:
    254         jpg_formatter.for_type(Figure, lambda fig: print_figure(fig, 'jpg', **kwargs))

~/.local/lib/python3.9/site-packages/IPython/core/pylabtools.py in retina_figure(fig, **kwargs)
    140 def retina_figure(fig, **kwargs):
    141     """format a figure as a pixel-doubled (retina) PNG"""
--> 142     pngdata = print_figure(fig, fmt='retina', **kwargs)
    143     # Make sure that retina_figure acts just like print_figure and returns
    144     # None when the figure is empty.

~/.local/lib/python3.9/site-packages/IPython/core/pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
    132         FigureCanvasBase(fig)
    133 
--> 134     fig.canvas.print_figure(bytes_io, **kw)
    135     data = bytes_io.getvalue()
    136     if fmt == 'svg':

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, pad_inches, bbox_extra_artists, backend, **kwargs)
   2253                 # force the figure dpi to 72), so we need to set it again here.
   2254                 with cbook._setattr_cm(self.figure, dpi=dpi):
-> 2255                     result = print_method(
   2256                         filename,
   2257                         facecolor=facecolor,

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/backend_bases.py in wrapper(*args, **kwargs)
   1667             kwargs.pop(arg)
   1668 
-> 1669         return func(*args, **kwargs)
   1670 
   1671     return wrapper

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/backends/backend_agg.py in print_png(self, filename_or_obj, metadata, pil_kwargs, *args)
    506             *metadata*, including the default 'Software' key.
    507         """
--> 508         FigureCanvasAgg.draw(self)
    509         mpl.image.imsave(
    510             filename_or_obj, self.buffer_rgba(), format="png", origin="upper",

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/backends/backend_agg.py in draw(self)
    404              (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar
    405               else nullcontext()):
--> 406             self.figure.draw(self.renderer)
    407             # A GUI class may be need to update a window using this draw, so
    408             # don't forget to call the superclass.

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/artist.py in 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()

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/figure.py in draw(self, renderer)
   2788 
   2789             self.patch.draw(renderer)
-> 2790             mimage._draw_list_compositing_images(
   2791                 renderer, self, artists, self.suppressComposite)
   2792 

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    130     if not_composite or not has_images:
    131         for a in artists:
--> 132             a.draw(renderer)
    133     else:
    134         # Composite any adjacent images together

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/_api/deprecation.py in wrapper(*inner_args, **inner_kwargs)
    429                          else deprecation_addendum,
    430                 **kwargs)
--> 431         return func(*inner_args, **inner_kwargs)
    432 
    433     return wrapper

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/axes/_base.py in draw(self, renderer, inframe)
   2919             renderer.stop_rasterizing()
   2920 
-> 2921         mimage._draw_list_compositing_images(renderer, self, artists)
   2922 
   2923         renderer.close_group('axes')

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    130     if not_composite or not has_images:
    131         for a in artists:
--> 132             a.draw(renderer)
    133     else:
    134         # Composite any adjacent images together

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/collections.py in draw(self, renderer)
   1010     def draw(self, renderer):
   1011         self.set_sizes(self._sizes, self.figure.dpi)
-> 1012         super().draw(renderer)
   1013 
   1014 

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/collections.py in draw(self, renderer)
    408                 mpath.Path(offsets), transOffset, tuple(facecolors[0]))
    409         else:
--> 410             renderer.draw_path_collection(
    411                 gc, transform.frozen(), paths,
    412                 self.get_transforms(), offsets, transOffset,

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/patheffects.py in draw_path_collection(self, gc, master_transform, paths, *args, **kwargs)
    128             # Call the base path effect function - this uses the unoptimised
    129             # approach of calling "draw_path" multiple times.
--> 130             return super().draw_path_collection(gc, master_transform, paths,
    131                                                 *args, **kwargs)
    132 

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/backend_bases.py in draw_path_collection(self, gc, master_transform, paths, all_transforms, offsets, offsetTrans, facecolors, edgecolors, linewidths, linestyles, antialiaseds, urls, offset_position)
    261                 transform = transform.frozen()
    262                 transform.translate(xo, yo)
--> 263             self.draw_path(gc0, path, transform, rgbFace)
    264 
    265     def draw_quad_mesh(self, gc, master_transform, meshWidth, meshHeight,

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/patheffects.py in draw_path(self, gc, tpath, affine, rgbFace)
     99     def draw_path(self, gc, tpath, affine, rgbFace=None):
    100         for path_effect in self._path_effects:
--> 101             path_effect.draw_path(self._renderer, gc, tpath, affine,
    102                                   rgbFace)
    103 

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/patheffects.py in draw_path(self, renderer, gc, tpath, affine, rgbFace)
    170     class withEffect(effect_class):
    171         def draw_path(self, renderer, gc, tpath, affine, rgbFace):
--> 172             super().draw_path(renderer, gc, tpath, affine, rgbFace)
    173             renderer.draw_path(gc, tpath, affine, rgbFace)
    174 

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/patheffects.py in draw_path(self, renderer, gc, tpath, affine, rgbFace)
    210         gc0.copy_properties(gc)
    211         gc0 = self._update_gc(gc0, self._gc)
--> 212         #renderer.draw_path(
    213         #    gc0, tpath, affine + self._offset_transform(renderer), rgbFace)
    214         gc0.restore()

~/.local/miniconda3/envs/py3.9_default/lib/python3.9/site-packages/matplotlib/backends/backend_agg.py in draw_path(self, gc, path, transform, rgbFace)
    159         else:
    160             try:
--> 161                 self._renderer.draw_path(gc, path, transform, rgbFace)
    162             except OverflowError as err:
    163                 raise OverflowError("Exceeded cell block limit (set "

SystemError: new style getargs format but argument is not a tuple

Expected outcome

The code to run without error.

Operating system

Linux/CentOS

Matplotlib Version

3.4.3

Matplotlib Backend

module://matplotlib_inline.backend_inline

Python version

3.9

Jupyter version

No response

Other libraries

No response

Installation

pip

Conda channel

No response

[QuLogic]

That seems reasonable; would you like to open a PR with that change?

[anntzer]

Actually I think the "correct" fix is e.g. #19563 (comment).